Genera included:

Aphanostephus DC.

Apopyros G.L. Nesom

Conyza Less.

Darwiniothamnus Harling

Erigeron L.

Hysterionica Willd.

Leptostelma D. Don

Neja D. Don

Erigeron L., Sp. Pl. 2: 863. 1753 [nom. conserv. prop.]. (see Heath, 1994)

Type: Erigeron uniflorus L. (M.L. Green, Prop. Brit. Bot. 181. 1929; W. Huber, Taxon 41: 563. 1992 - Herb. Linn., No. 994.23, typ. conserv. prop.) (also see comments in Nesom, 1989c).

Infrageneric groups were recognized for most of the New World species by Nesom (1989c), and others have subsequently been added (Nesom and Noyes, 1999; Nesom, 1990c, 1994a). The analysis of Noyes (2000a) and recent work on the species-level taxonomy of Erigeron for the FNA treatment (Nesom, 2006) have indicated that some of the groups of Erigeron earlier recognized by Nesomare not monophyletic. This reflects the misplacement of individual species, but in larger part it results from recognition of a number of over-broadly defined groups. For example, informally treated subgroups of sect. Asteroidea do not cohere as a single phyletic element, sect. Olygotrichium and sect. Fruticosus include evolutionarily disparate subgroups of species, and sect. Geniculactis (sensu Nesom, 1990c) comprises two separate groups. More strictly defined groups convey a better understanding of the evolutionary patterns and distribution of diversity within the genus. Eventual refinement of the phylogenetic arrangement of these groups may suggest or require additional categories and the composition and rank of some groups may be altered, depending on philosophical point-of-view and development of further data useful for systematic interpretation.

Erigeron as treated here includes about 400 species. 304 are New World species (enumerated below); Old World species are estimated to be around 80–100 (most numerous in eastern Asia and Russia). Figures 2–7 illustrate various aspects of habit and floral diversity in the genus.

1. Sect. Arenarioides (Rydb.) Nesom, Phytologia 67: 70. 1989. Erigeron [unranked sp. group] Arenarioides Rydb., Fl. Rocky Mts. 897. 1918, in clave. TYPE: Erigeron arenarioides (D.C. Eaton ex A. Gray) A. Gray ex Rydb.

Taprooted, perennial; caudex branching, retaining old leaf bases; glabrous; stems branched; leaves filiform or linear to linearoblanceolate, not clasping; heads erect in bud; rays white, often with an abaxial midstripe, not coiling or reflexing; achenes 1.5–2.2 mm long, 2-nerved; pappus of 10–16 bristles.

E. arenarioides (D.C. Eaton ex A. Gray)

A. Gray ex Rydb.

E. salmonensis Brunsfeld & Nesom

Erigeron salmonensis was recently described (Brunsfeld and Nesom, 1989); the two species of sect. Arenarioides were regarded as closely related but isolated within the genus. Molecular data (Noyes, 2000a) indicate that E. tweedyi Canby (sect. Spathifolium) is closely related to E. arenarioides - with this molecular pointer, morphological similarities between sect. Spathifolium and sect. Arenarioides are apparent, but sect. Spathifolium, as represented by E. tener, is placed by the molecular data most closely related to sect. Osteocaulis.

2. Sect Asterigeron Rydb., Fl. Rocky Mts. 891. 1918. TYPE: Erigeron watsonii Erigeron sect. Spathifolium Nesom, Phytologia 67: 84. 1989. TYPE: Erigeron tener (A. Gray) A. Gray

Perennial, taprooted; caudex simple or more commonly a multicipital crown or with elongating branches, forming mats (E. acomanus, E. tener) connected by systems of lignescent rhizomes and caudex branches; vestiture short-strigillose to villous, hirsute, or glabrous, hairs white (E. tener, E. acomanus, E. tweedyi, and E. wilkenii have similar vestiture; E. cronquistii, E. evermannii, E. subglaber glabrous to glabrate); stems branching (simple in E. acomanus, E. wilkenii); leaves spatulate to oblanceolate, entire, with expanded and indurate petiole bases, often folding, not clasping; heads 1 or 1–3, nodding in bud (E. acomanus, E. tweedyi), behavior unknown in others; phyllaries with a broad green midband, minutely glandular; rays white to pink, not coiling (or coiling in E. garrettii?) or reflexing; achenes 1.5–3.2 mm long (1–1.2 in E. cavernensis, 3.2–3.5 mm in E. evermanii), 2-nerved; pappus of 10–35 bristles.

Group A. U.S.A.; leaves thin, longpetioled, vestiture relatively sparse.

E. cavernensis S.L. Welsh & N.D. Atwood

E. cronquistii Maguire

E. evermannii Rydb.

E. uncialis Blake (incl. E. conjugans Blake)

E. watsonii (A. Gray) Cronquist

Group B. U.S.A.; leaves thick, shortpetioled; vestiture closely white-strigillose.

E. acomanus Spellenb. & P. Knight

E. tener (A. Gray) A. Gray

E. tweedyi Canby

E. wilkenii O'Kane (O'Kane 1990)

Group C. U.S.A.; leaves thick, shortpetioled; glabrous to glabrate; caudex multicipital.

E. garrettii Rydb.

E. subglaber Cronquist

Group D. Mexico.

E. cuatrocienegensis G.L. Nesom

E. gypsoverus G.L. Nesom

E. unguiphyllus G.L. Nesom

Molecular data (Noyes, 2000a) indicate that E. tweedyi is closely related to E. arenarioides (sect. Arenarioides), but the closer morphological associates of E. tweedyi instead seem to be in sect. Spathifolium. Noyes's data also suggest that sect. Spathifolium (as represented by E. tener) may be closely related to sect. Osteocaulis. The vestiture in sect. Spathifolium is similar to that of sects. Wyomingia, Arenarioides, and Osteocaulis, but the species in the latter sections produce conspicuously coiling rays. There also are suggestive similarities between sect. Spathifolium and sect. Asterigeron.

Erigeron subglaber has leaves oblanceolate to broadly oblanceolate or subspatulate and differs from the other U.S.A. species, which usually have distinctly spatulate leaves. This species apparently exists only as a single population system on the Elk Mountain Ridge of the Sangre de Cristo Mountains in San Miguel Co., New Mexico (ESE of Cowles, ca. 10,000–11,500 ft elevation). If not a member of sect. Spathifolium, it apparently is isolated geographically as well as morphologically from other possible close relatives (except one) within the genus. The identification of the original collection was E. leiomerus (sect. Asterigeron), to which it is similar but which has nodding buds and reflexing rays; the assessment of these behaviors in E. subglaber is based on somewhat ambiguous observations of herbarium specimens and online photographs. Erigeron garrettii appears to be very similar to E. subglaber, and they are placed here as closely related despite their considerable separation in geography.

The species of Group B are gypsophilic endemics of northeastern Mexico (Coahuila, Nuevo León, and San Luis Potosí, respectively), tentatively placed in sect. Spathifolium emphasizing their short-strigillose vestiture and ray behavior. They are geographically disjunct from the more typical members of the section; the closest species of the section sensu stricto is E. acomanus from northwestern New Mexico. None of the other species of northeastern Mexico show features that suggest that they might have been the immediate forebearers of E. cuatrocienegensis and E. gypsoverus.

3. Sect. Asteroidea Nutt., Trans. Amer. Philos. Soc. ser. 2, 7: 308. 1841. LECTOTYPE): Erigeron decumbens Nutt. (Nesom, 1989c)

Erigeron [unranked sp. group] Decumbentes Rydb., Fl. Colorado 359. 1906, in clave. TYPE: Erigeron decumbens Nutt.

Erigeron [unranked sp. group] Asperuginei Rydb., Fl. Rocky Mts. 897. 1918, in clave. TYPE: Erigeron asperugineus (D.C. Eaton) A. Gray

Perennial, taprooted; caudex branches generally slender (rhizome-like in E. decumbens); sparsely to densely strigillose or strigose to hirsute or hirtellous, stems and involucres often minutely glandular; stems simple or branched, basally ascending to decumbent; leaves linear to oblanceolate or subspatulate, entire, usually with indistinct petiole region, usually 3-nerved, cauline gradually reduced, not clasping; heads 1–7+, commonly more than 1, erect in bud; rays white to blue, not coiling or only weakly so; achenes 1.2–3.5(-4.5) mm long, 2-nerved; pappus of (6-)12–30 bristles.

E. asperugineus (D.C. Eaton) A. Gray

E. canaani S.L. Welsh (incl. E. higginsii S.L. Welsh)

E. corymbosus Nutt.

E. decumbens Nutt.

E. eatonii A. Gray (incl. E. sonnei Greene, E. nevadincola Blake)

E. jonesii Cronquist (incl. E. wahwahensis S.L. Welsh, see Cronquist 1994)

E. lassenianus Greene (incl. E. flexuosus Cronquist)

E. maniopotamicus G.L. Nesom & T. Nelson

E. robustior (Cronquist) G.L. Nesom

Sect. Asteroidea previously was interpreted to include a broader array of species and species groups (Nesom, 1989c), but it is here limited to the strict sense (the “Erigeron decumbens group” of Nesom, 1989), following indications of molecular data (Noyes, 2000a). Studies of this group of species have recently been published (Strother and Ferlatte 1988; Nesom, 1992b, 1992c, 2004); E. maniopotamicus is newly described (Nesom and Nelson, 2004).

Molecular evidence (Noyes, 2000a) suggests that Erigeron aliceae is most closely related to species of sect. Asteroidea but it is closer in morphology to sect. Fruticosus, especially in its fibrous-rooted rhizomes, clasping leaves, villous involucres, coiling rays, and relatively large, 2(-4)-nerved achenes.

Erigeron asperugineus has a set of features common to sect. Asteroidea: slender-taprooted with a simple or branched caudex, stems decumbent-ascending, leaves mostly basal, spatulate, and 1-nerved or weakly 3-nerved, heads 1(-2), phyllaries often purple, sparsely to moderately hirsutulous, densely minutely glandular, rays blue, not coiling or reflexing, achenes 2.5–3.1 mm, and pappus bristles 20–30. The hirtellous vestiture is more like sect. Pseuderigeron; the often strongly petiolate-spatulate leaves are suggestive of Group A of sect. Asterigeron. The range of E. asperugineus in Idaho, Montana, Nevada, and Utah is more similar to species of section Radicati.

4. Sect. Cincinnactis Nesom, Phytologia 67: 73. 1989. TYPE: Erigeron longipes DC.

Fibrous-rooted, rhizomatous (taprooted in E. oaxacanus), perennial (annual in E. narcissus); caudex simple or divided into slender, rhizomelike branches; vestiture; stems simple, rarely branched; leaves ovatelanceolate, ovate-lanceolate, clasping or subclasping; heads erect (?) in bud; rays (80-) 120–350, mostly filiform, white, tightly coiling at maturity; achenes ca 0.6–1 mm long, 2-nerved; pappus of 12–23 bristles (absent or reduced in number in E. narcissus).

E. longipes DC.

E. narcissus G.L. Nesom

E. oaxacanus Greenm.

E. procumbens (Houston ex Mill.) G.L. Nesom (syn = E. myriactis Small)

E. stanfordii I.M. Johnst. ex Nesom

E. tephropodus G.L. Nesom

Erigeron stanfordii is placed here because of its tightly coiling rays (see images of isotypes at MO, NY), although the laminae are distinctly wider and fewer (45–76) and the achenes longer (2 mm long) than in the other species of Cincinnactis. Molecular data (Andrus et al., sin prep.), in contrast, suggest that E. stanfordii is phyletically basal-most or near it in the whole genus, far separated from the species of sect. Cincinnactis.

Erigeron basilobatus and E. veracruzensis, placed in sect. Cincinnactis in 1989, are transferred here to sect. Quercifolium, as suggested by the molecular data of Noyes (2000a). The group of Caribbean species with tightly coiling rays, including E. bellioides and E. cuneifolius and placed by Nesom (1989) within sect. Cincinnactis, is here treated as sect. Microcephalum. Erigeron exilis has been transferred to sect. Lamprocaules G.L. Nesom & R.D. Noyes (Nesom and Noyes, 1999). Erigeron crenatus and E. socorrensis are transferred to sect. Caenotis.

5. Sect. Disparipili Nesom, sect. nov.

Vestimento caulino trichomatibus patentibus in longitudine valde inequali, capitulis in alabastro erectis, et radiis cincinatis distinctus. TYPE: Erigeron disparipilus Cronquist

Taprooted, perennial; caudex simple; cauline vestiture with spreading hairs of markedly unequal length (E. chrysopsidis, E. disparipilis, E. poliospermus); stems simple or branched; leaves narrowly oblanceolate and 1-nerved, entire, not clasping, mostly basal, or cauline well-developed; leaf margins/ petioles coarsely ciliate; heads erect in bud or on arching peduncles; rays present (absent in E. chrysopsidis var. austiniae), white (yellow in E. chrysopsidis, E. piperianus), coiling; achenes 1.6–1.8 mm (E. piperianus) to 2.1–3 mm to 3.5–4.5 mm (E. latus) long, 2-nerved; pappus of 14–30 bristles.

E. chrysopsidis A. Gray

E. davisii (Cronquist) G.L. Nesom

E. disparipilus Cronquist

E. latus (A. Nelson & J.F. Macbr.) Cronquist

E. nanus Nutt.

E. piperianus Cronquist

E. poliospermus A. Gray

Cronquist (1994) hypothesized that Erigeron nanus (and E. rydbergii Cronquist) are closely related to E. untermannii S.L. Welsh but the latter is placed here in sect. Wyomingia. The distinction of E. davisii and its relationship to this group were noted by Nesom (2004).

6. Sect. Erigeridium Torr. & A. Gray, Fl. N. Amer. 2(1): 176. 1841. TYPE: Erigeron vernus (L.) Torr. & A. Gray

Fragmosa Raf., Fl. Tellur. 2: 50. 1836. LECTOTYPE (Nesom 1989c): Erigeron nudicaulis Michx. (= Erigeron vernus (L.) Torr. & A. Gray)

Erigeron [unranked sp. group] Verni Small, Man. Southeastern Fl. 1395. 1933, in clave. TYPE: Erigeron vernus (L.) Torr. & A. Gray

Fibrous-rooted, perennial, sometimes rhizomatous or stoloniferous; caudex simple; glabrous to sparsely strigose or hispid; stems simple or branched; leaves obovate to spatulate, often thick, entire or shallowly toothed, not clasping; heads erect in bud; rays white, not coiling or reflexing; achenes 1.2–1.6 mm, 4-nerved; pappus of 16–30 bristles.

E. hintoniorum G.L. Nesom

E. morelensis Greenm.

E. palmeri A. Gray

E. vernus (L.) Torr. & A. Gray

E. wellsii G.L. Nesom

This group of species was earlier included within the primarily western U.S.A. sect. Fruticosus (Nesom, 1989c) as the “E. palmeri group.” The apparent morphological coherence of these five species, however, and the geographic range divided between the eastern USA and the eastern sierra of Mexico, also characteristic of other groups in various genera, indicate that sectional status is appropriate for the E. palmeri group. Species of sect. Erigeridium have not yet been included in molecular studies.

7. Sect. Erigeron

Erigeron sect. Uniflori G. Don in Loudon, Hort. Brit. 343. 1830. TYPE: Erigeron uniflorus L.

Aster sect. Pauciflori G. Don in Loudon, Hort. Brit. 346. 1830. LECTOTYPE: Aster pulchellus Willd. (= Erigeron venustus Botsch.) (Sundberg and Jones, 1987)

Erigeron [unranked sp. group] Uniflori Rydb., Fl. Colorado 359. 1906, in clave. TYPE: Erigeron uniflorus L.

Erigeron sect. Monocephali Vierh., Beih. Bot. Centralbl. 19: 492. 1906. LECTOTYPE (Nesom 1989c): Erigeron uniflorus L.

Erigeron sect. Siphonoglossa Botsch., Bot. Mater. Gerb. Bot. Inst. Komarova Akad. Nauk SSSR 16: 393. 1954. TYPE: Erigeron Uniflorus

Erigeron sect. Platyglossa Botsch., Bot. Mater. Gerb. Bot. Inst. Komarova Akad. Nauk SSSR 16: 388. 1954. TYPE: Erigeron venustus Botsch.

Perennial; fibrous-rooted, usually from a short, suberect rhizome; caudex simple or with short, thick branches; strigose to hirsute or villous; stems simple; leaves mostly basal oblanceolate to obovate or spatulate, entire, not clasping; heads 1, erect in bud; rays white or blue (yellow in E. aureus), coiling (not coiling in E. uniflorus); achenes 1.6–2.8 mm long, 2-nerved; pappus of (7-)10–30 bristles (accrescent in E. uniflorus).

North America

E. algidus Jeps. (incl. E. petiolaris Greene, see Nesom, 1992b, 1992c)

E. aureus Greene

E. alpiniformis Cronquist

E. X arthurii Boivin

E. denalii A. Nelson

E. eriocephalus J. Vahl

E. flettii G.N. Jones

E. grandiflorus Hooker (incl. E. simplex Greene)

E. hultenii Spongberg (status uncertain; Nesom and Murray 2004)

E. humilis Graham

E. hyperboreus Greene (incl. E. alaskanus Cronquist)

E. melanocephalus A. Nelson

E. muirii A. Gray

E. porsildii Nesom & D. Murray

South America (The E. andicola DC. complex, see Solbrig, 1962)

Erigeron andicola DC.

Erigeron ciliaris Phil.

Erigeron cinereus Hook. & Arn.

Erigeron incertus (d'Urville) Skottsb.

Erigeron lanceolatus Wedd.

Erigeron leptopetalus Phil.

Erigeron myosotis Pers.

Erigeron patagonicus Phil.

Erigeron pratensis Phil.

Eurasia (China and Russia not represented)

E. anisophyllus Rech. f.

E. caucasicus Steven

E. cedretorum Rech. f.

E. cilicicus Boiss. ex Vierh.

E. daenensis Vierh.

E. eriocalyx (Ledeb.) Vierh.

E. hyrcanicus Bornm. & Vierh.

E. komarovii Botsch.

E. koraginensis (Komarov) Botsch.

E. miyabeanus Tatew. & Kitam.

E. multiradiatus (DC.) C.B. Clarke

E. petroiketes Rech. f.

E. plesiogeron Rech. f.

E. pseuderiocephalus M. Popov

E. silenifolius (Turcz.) Botsch.

E. thunbergii A. Gray

E. uniflorus L.

E. zederbaueri Vierh.

Molecular data (Noyes, 2000a) indicate that the species of sect. Trimorpha (at least the European species Erigeron acris and E. borealis) are more closely related to E. uniflorus and to E. grandiflorus (incl. E. simplex) than they are to a group of American species including E. flettii, E. humilis, E. cinereus, and E. lonchophyllus. In fact, sect. Trimorpha and sect. Erigeron sensu stricto appear to be more closely related to sect. Rhizonexus than to the latter group of sect. Erigeron. The implication of this is that sect. Erigeron (as outlined above) is biphyletic. The amphi-Atlantic E. humilis, however, is hypothesized to have arisen as an allotetraploid offspring of a cross between E. uniflorus and a species similar to E. melanocephalus and E. hyperboreus (Engelskjön, 1967; Spongberg, 1971). In the Noyes analysis, the Andean taxa of South America are represented by E. cinereus.

Among the North American taxa, Erigeron uniflorus alone has accrescent pappus bristles, a feature shared with the species of sect. Trimorpha.

8. Sect. Filifolii (Rydb.) Nesom, comb. et stat. nov. Erigeron [unranked sp. group] Filifolii Rydb., Fl. Rocky Mts. 897. 1918, in clave. TYPE: Erigeron filifolius Nutt.

Perennial, taprooted; caudices multicipital, often with relatively short and thin, stemlike, lignescent branches; sparsely to densely strigose with loosely appressed to ascending, fine hairs, densely white-strigose at least proximally; leaves linear to filiform, basal (not in a rosette) and cauline (gradually or little reduced distally); heads 1–5(-10+) from distal branches, in loosely corymbiform arrays, erect in bud; rays weakly coiling; achenes 1.4–1.8(-2) mm long, 2-nerved.

Erigeron filifolius Nutt.

Erigeron filifolius has features in common with sect. Wyomingia (but is geographically displaced and ecologically incongruent and lacks the multinerved achenes of the multi-headed species) and sect. Osteocaulis (but lacks the characteristic indurate-sheathing leaf bases) and some features in common with Group A of sect. Asteroidea. It is without obvious near-sister species and placed here in a monotypic section, with speculation that its closest relatives are geographically close, perhaps those of sect. Osteocaulis.

9. Sect. Fruticosus G. Don in Loudon, Hort. Brit. 343. 1830. TYPE: Erigeron glaucus Ker-Gawler

Woodvillea DC., Prodr. 5: 318. 1836. TYPE: Erigeron glaucus Ker-Gawler

Erigeron sect. Phoenactis Nutt., Trans. Amer. Philos. Soc. ser. 2, 7: 310. 1841. LECTOTYPE (Nesom, 1989c): Erigeron speciosus (Lindl.) DC.

Erigeron [unranked sp. group] Elatiores Rydb., Fl. Colorado 359. 1906, in clave. TYPE: Erigeron elatior (A. Gray) Greene

Erigeron [unranked sp. group] Salsuginosi Rydb., Fl. Colorado 359. 1906, in clave. TYPE: Erigeron salsuginosus (Rich.) A. Gray (= E. peregrinus subsp. callianthemus (Greene) Cronq. = E. glacialis Nutt.)

Erigeron [unranked sp. group] Macranthi Rydb., Fl. Colorado 359. 1906, in clave. TYPE: Erigeron macranthus Nutt. (= E. speciosus)

Erigeron [unranked sp. group] Glabelli Rydb., Fl. Colorado 359. 1906, in clave. TYPE: Erigeron glabellus Nutt.

Erigeron [unranked sp. group] Asperi Rydb., Fl. Rocky Mts. 897. 1918, in clave. TYPE: Erigeron asper Nutt. (= E. glabellus)

Erigeron sect. Peregrinus Nesom, Syst. Bot. 7: 463. 1982. TYPE: Erigeron peregrinus (Pursh.) Greene

Perennial, fibrous-rooted, rhizomatous, sometimes with stolons; caudex branched; glabrate to strigose, hirsute, or villous; stems usually branched; leaves oblanceolate to spatulate, entire or toothed cauline nearly even-sized upward, clasping to subclasping; heads 1 (E. howellii) or 1–15(-22) in a loosely corymbiform arrangement, nodding in bud (apparently erect in E. aliceae, E. glaucus, E. glacialis); rays white to blue or pink, weakly coiling or not at all; achenes 1.1–3 mm long; pappus of 14–32 bristles.

Group A. Basal leaves persistent; achenes 2-nerved (E. arizonicus, E. cervinus, E. formosissimus, E. glabellus, E. yukonensis) or mostly 2(-4)-nerved (E. aliceae, E. eximius, E. glaucus, E. potosinus) or (4-)5(-7)-nerved (E. glacialis, E. howellii, E. peregrinus); buds apparently erect (E. aliceae, E. cervinus, E. glacialis, E. glaucus), or nodding? (E. formosissimus).

E. aliceae Howell

E. arizonicus A. Gray

E. cervinus Greene (incl. E. delicatus Cronquist)

E. eximius Greene

E. formosissimus Greene

E. glabellus Nutt.

E. glacialis Nutt. (syn = E. peregrinus var. callianthemus (Greene) Cronquist)

E. glaucus Ker-Gawler

E. howellii A. Gray

E. peregrinus (Pursh) Greene

E. potosinus Standl.

E. thunbergii A. Gray complex (Asia)

E. yukonensis Rydb. (syn = E. glabellus var. yukonensis (Rydb.) Hultén)

Group B. Basal leaves persistent; achenes 2-nerved or 2(-4)-nerved; buds nodding (E. coulteri, E. rybius), behavior unknown in others.

E. coulteri Porter

E. rybius G.L. Nesom

E. hessii G.L. Nesom

E. kuschei Eastw.

Group C. Basal leaves scalelike or not strongly differentiated; achenes 2-nerved or 2(-4)-nerved; buds nodding.

E. elatior (A. Gray) Greene

E. speciosus (Lindl.) DC.

E. subtrinervis Rydb.

E. uintahensis Cronquist

E. vreelandii Greene (incl. E. platyphyllus Greene)

Erigeron yukonensis is rhizomatous and fibrous-rooted, although the caudices or rhizomes sometimes resemble taproots. Hultén (1968) considered it to be closely related to E. glabellus.

Molecular evidence (Noyes, 2000a) indicates that Erigeron aliceae is most closely related to species of sect. Asteroidea, but it is closer in morphology to sect. Fruticosus, especially in its fibrous-rooted and rhizomatous habit, clasping leaves often relatively large and even-sized up the stem, villous involucres, non-coiling rays, and relatively large (2–2.8 mmlong), 2(-4)-nerved achenes.

Erigeron arizonicus is rhizomatous and fibrous-rooted but the caudices or rhizomes are relatively thick and sometimes resemble a taproot; basal leaves are usually persistent, spatulate, obovate to ovate, or elliptic, and cauline leaves are subclasping, but they often are 3-nerved and have shallowly serrate margins, features unusual in Group A of sect. Fruticosus.

Erigeron cervinus is relatively isolated, as early observed by Cronquist (1947, p. 217), who noted that “Aside from E. cervinus, [E. delicatus] has no very close relatives known to me.” For E. cervinus he noted that it is “probably derived from E. peregrinus, but the connection is now remote.”

10. Sect. Geniculactis Nesom, Phytologia 69: 250. 1990. TYPE: Erigeron coronarius Greene

Taprooted, annual or short-perennial; caudex simple; hirsute to hispid; stems branched; leaves linear to linear-oblong, -lanceolate, or -oblanceolate, not clasping, entire to toothed, rarely lobed; heads erect in bud; disc corollas often prominently inflated above the short tube; rays 40–200, white, reflexing or (in Erigeron sceptrifer) downward curving-reflexing, barely longer than the involucre in E. zacatensis; achenes 0.5–1 mm long, 2-nerved (orange); pappus of 2–17 bristles or (in E. reinana) absent. E. reinana has relatively few, loosely coiling rays and uninflated disc corollas.

E. arisolius G.L. Nesom

E. coronarius Greene

E. janivultus G.L. Nesom

E. reinana G.L. Nesom

E. sceptrifer G.L. Nesom

E. zacatensis G.L. Nesom

The species of sect. Geniculactis are restricted to Mexico, except for two that also occur in southern Arizona - E. arisolius and E. sceptrifer. Erigeron reinana was recently added to the group (Nesom, 1998). The E. pumilus group was tentatively included in the original circumscription of sect. Geniculactis (Nesom, 1990c) but is here treated separately as sect. Stenactis Cass.

Erigeron reinana is recognized by its taprooted habit, coarse vestiture, narrow, entire leaves, numerous heads on short peduncles, erect buds, loosely coiling rays, and much reduced, essentially bristle-less pappus. It differs from E. coronarius and the other species of sect. Geniculactis in its fewer, loosely coiling rays and uninflated disc corollas; it might be placed with less technical/diagnostic anomaly in sect. Imbarba, but the vestiture, leaf morphology, and capitulescence of E. reinana are more similar to sect. Geniculactis.

11. Sect. Geronpternix Nesom & Noyes, Sida 18: 1163. 1999. TYPE: Erigeron rhizomatus Cronquist

Perennial, rhizomatous, with thick fibrous roots, rhizomes or rhizomelike caudex branches creeping-ascending; slender, scaleleaved, without well-defined central axes; strigose to strigose-hirsutulous; stems simple or 1–3 branched; leaves cauline, mostly linear at midstem, entire, not clasping; heads 1(-3), nodding or erect in bud; rays with abaxial lilac midstripe, not coiling or reflexing; achenes 3.5–4.5 mm long, 2–4-nerved (E. lepidopodus) or 5–6-nerved (E. rhizomatus); pappus of 25–50 bristles.

E. lepidopodus (B.L. Rob. & Fernald) G.L. Nesom

E. rhizomatus Cronquist

These two species, previously hypothesized to be sister species (Nesom, 1989c), were tentatively treated as members of the E. foliosus group (sect. Pycnophyllum) in the Nesom (1989c) overview of Erigeron but were shown by Noyes (2000a) to be the phyletically basalmost species of the Conyzinae. As noted by Noyes (2000a, p. 106), these two species are characterized by a “4-bp insertion that is shared with outgroup taxa Chrysopsis and Heterotheca and with all other Astereae, but that is absent in all other Conyzinae.”

12. Sect. Gyrifolium Nesom, sect. nov.

Radice palari crassa, foliis basalibus persistentibus spatulati-obovatis, capitulis in alabastro erectis(?), et radiis leniter cincinatis vel noncincinatis distinctus. TYPE: Erigeron oreganus A. Gray

Perennial, taprooted (stout); caudex branches short, thick; hirsute to villous, stipitate-glandular or minutely glandular; stems simple or branched; basal leaves persistent, spatulate-obovate, 1(-3)-nerved, toothed, cauline leaves little reduced upward (clasping to subclasping in E. cascadensis, E. leibergii); heads usually 1 but sometimes 2–4 more developed from lower axils, erect? in bud; phyllaries relatively broad, erect, and even-length; rays white, coiling but sometimes weakly or not at all; disc corollas with long (1.2–1.5 mm) tubes; achenes 1.2–2.2 mm long, 2-nerved; pappus of 12–20 bristles.

E. cascadensis A.A. Heller

E. leibergii Piper

E. oreganus A. Gray

The species of sect. Gyrifolium are rare and grow on ledges and cliffs in western Washington, Oregon, and British Columbia. They were previously placed within sect. Fruticosus, emphasizing the relatively welldeveloped and subclasping cauline leaves, but the taproot and other features (caudex, leaves, ray corollas, and phyllaries) suggest that the two groups are not so closely related. The name (‘gyrifolium’) alludes to a resemblance of a spinning top to the whorl of basal leaves atop a thick taproot.

13. Sect. Imbarba Nesom, Phytologia 67: 78. 1989. TYPE: Erigeron galeottii (A. Gray ex Hemsl.) Greene

Perennial (annual in E. strigulosus), rhizomatous (sometimes taprooted in E. strigulosus), sometimes with basal offsets or producing stolons or runners; caudex simple or branched; glabrous to sparsely strigose, hirsute, or pilose; stems simple or fewbranched; leaves spatulate to oblanceolate, entire or toothed, cauline clasping to subclasping or not clasping; heads erect in bud; rays white, weakly coiling; achenes 1–3 mm long, 2-nerved; pappus a fimbriolate or scaley crown, bristles absent or occasionally a few, short, vestigial bristles present, or pappus in E. macdonaldii of 5–7 short, persistent bristles 1/2–2/3 as long as the disc corollas.

E. astranthioides De Jong & G.L. Nesom

E. forreri (Greene) Greene

E. fraternus Greene

E. galeottii (A. Gray ex Hemsl.) Greene

E. guatemalensis (Blake) G.L. Nesom

E. macdonaldii G.L. Nesom

E. mimus (Blake) G.L. Nesom

E. quiexobrensis G.L. Nesom

E. strigulosus Greene

Two new species have been added to sect. Imbarba after the Nesom (1989c) overview: E. macdonaldii (Nesom, 1990d) and E. quiexobrensis (Nesom, 1990e). All species of the section are restricted to Mexico and Central America. Sect. Imbarba and sect. Geniculactis are the closest relatives of most South American Conyzinae, according to the molecular data of Noyes (2000a).

14. Sect. Karvinskia Nesom, Phytologia 67: 79. 1989. TYPE: Erigeron karvinskianus DC.

Perennial (annual in E. barbarensis), taprooted (E. barbarensis, E. karvinskianus, E. irazuensis, E. pacayensis?) or rhizomatous (E. aquarius, E. fluens, E. heteromorphus); caudex simple; strigose to hirsute; stems branched; leaves spatulate to oblanceolate or linear, entire or toothed, not clasping; heads erect in bud; rays white, becoming lavender at maturity, slightly coiling or not at all; achenes 1–1.9 mm long, 2-nerved; pappus of 10–27 bristles.

E. aquarius Standl. & Steyerm.

E. barbarensis Nesom & T.R. Van Devender

E. fluens G.L. Nesom

E. heteromorphus B.L. Rob.

E. irazuensis Greenm.

E. karvinskianus DC.

E. pacayensis Greenm.

Two new species have recently been added to sect. Karvinskia (Nesom 1998; Nesom and Van Devender, 2007). The native range of these species is restricted to Mexico and Central America; Erigeron karvinkianus has become a worldwide weed in tropical and subtropical latitudes. Erigeron pacayensis appears to be sometimes taprooted, sometimes rhizomatous.

15. Sect. Lamprocaules Nesom, Phytologia 76: 99. 1994. TYPE: Erigeron pattersonii G.L. Nesom

Perennial, fibrous-rooted, slender-rhizomatous (taprooted in E. tuerckheimii); caudex divided into short or slender, rhizomelike branches; glabrous to sparsely strigose; stems simple or branched, glabrate, shiny; leaves coriaceous, basal (apparently produced only in E. chiangii) spatulate to oblanceolate, entire to shallowly few-toothed, cauline filiform to linear to narrowly elliptic, not clasping; heads erect in bud; rays white, weakly coiling or not at all; achenes 0.8–1.8 mm long, 2-nerved; pappus of 11–22 bristles.

E. chiangii G.L. Nesom

E. exilis A. Gray

E. pattersonii G.L. Nesom

E. scoparioides G.L. Nesom

E. tuerckheimii Urb. (incl. E. ocoensis Urb. & Eckman?)

Erigeron exilis was recently transferred to sect. Lamprocaules from sect. Cincinnactis (Nesom and Noyes, 1999).

Erigeron tuerckheimii is endemic to the Caribbean island of Hispaniola. The plants are small shrubs up 20 cm tall, from a woody taproot producing thick branches with persistent old leaves. The leaves are linear to nearly filiform, with a hard, shiny texture, purple at the base, and are very densely arranged on the stems. The heads are solitary on naked or few-bracteate peduncles. Rays are white, apparently neither coiling nor reflexing. There is no other Caribbean species similar to it (except the possibly conspecific E. ocoensis), and it is placed here with this group of Mexican species on the basis of their similarity in leaf morphology. Erigeron tuerckheimii is comparable in habit to species of Neja, but the achenes are flat and 2-nerved, in contrast to those of Neja, which are terete and multi-nerved.

16. Sect. Linearifolii (G. Don) Nesom, Phytologia 67: 79. 1989.

Aster sect. Linearifolii G. Don in Loudon, Hort. Brit. 346. 1830. LECTOTYPE: Erigeron hyssopifolius Michx. (Sundberg and Jones, 1987)

Perennial, rhizomatous, fibrous-rooted; caudices sometimes branched; strigose to strigose-villous; stems branched; basal and proximal cauline leaves much reduced or present as scales, cauline blades linear to linear-oblong or oblong-lanceolate, not clasping; heads erect in bud; rays white, not coiling or reflexing; achenes 1.3–1.6 mm long, 5–6-nerved; pappus of 25–35 bristles.

E. hyssopifolius Michx.

This species of northern North America has been regarded as closely similar to the primarily Californian Erigeron foliosus group, treated here as sect. Pycnophyllum Cronquist (Cronquist, 1947; Nesom, 1989c, 1992a), but E. hyssopifolius was regarded as more isolated and formally segregated as a monotypic section by Nesom and Noyes (1999).

17. Sect. Lonchophylli Nesom, sect. nov.

Habitu fibrosi-radicato non-rhizomato, caudice simplici, capitulis plerumque 3–12 plerumque in dispositione laxe racemiformi in alabastro erectis, radiis filiformibus nonreflexis noncincinatis involucro parum longioribus distinctus. TYPE: Erigeron lonchophyllus Hook.

Biennial or short-lived perennial (sometimes appearing annual), fibrous-rooted, not rhizomatous; caudex simple; sparsely to densely hirsute, eglandular; stems branched; basal leaves oblanceolate to spatulate, entire, cauline mostly linear, not clasping; heads 1 or 3–12 usually in a loosely racemiform arrangement, erect in bud; rays white to pink, filiform, slightly longer than the involucre, not reflexing or coiling; achenes 1.3–1.8 mm, 2-nerved; pappus of 20–30 nonaccrescent bristles.

E. lonchophyllus Hook.

Erigeron lonchophyllus is similar to species of sect. Trimorpha in its fibrousrooted habit, narrow involucres in a racemiform arrangment, filiform suberect rays, and it was earlier included in sect. Trimorpha (Nesom 1989c). It lacks, however, the inner zone of eligulate pistillate florets characteristic of sect. Trimorpha, and molecular data (Noyes, 2000a) indicate that it is more closely related to a group of American species including E. flettii, E. humilis, and E. cinereus, placed here in sect. Erigeron.

18. Sect. Meridionales G.L Nesom & N. Andrus, sect. nov.

Habitu rhizomato fibrosi-radicato, capitulis solitariis in pedunculis scaposis vel plerumque in dispositione laxe corymbi-formi in alabastro erectis distinctus. TYPE: Erigeron fasciculatus Colla

Perennial herbs or subshrubs, rhizomatous, fibrous-rooted; caudex simple or multicipital; glabrous to strigose or villous; stems branched; leaves oblanceolate to lanceolate, entire to toothed or lobed, not clasping; heads 1 on scapose peduncles (Erigeron othonnifolius, E. turricola) or mostly in loosely corymbiform arrays, erect in bud; rays white to purple, not coiling or reflexing; achenes 1–4 mm long (0.5–1.0 mm in D. alternifolius), 2(-3)-nerved; pappus of [not counted] bristles.

Darwiniothamnus alternifolius Lawesson & Adsersen

Erigeron campanensis Valdeb., Lowrey, & Stuessy

Erigeron chionophilus Wedd.

Erigeron ecuadoriensis Hieron.

Erigeron fasciculatus Colla

Erigeron incaicus Solbrig

Erigeron luxurians (Skottsb.) Solbrig

Erigeron othonnifolius Hook. & Arn.

Erigeron paramensis Aristeg. & Cuatrec.

Erigeron raphaelis Cuatrec.

Erigeron rosulatus Wedd. status unknown:

Erigeron adscendens Turcz. (Ecuador)

Erigeron apiculatus Benth. (Ecuador)

Erigeron (Aster) gilliesii (Hook. & Arn.) Cabrera (Patagonia)

Erigeron pauper Benoist (Ecuador)

Molecular evidence (Andrus et al., in prep.) suggests that sect. Meridionales may not be monophyletic. Erigeron ecuadoriensis is indicated by molecular data (Andrus et al., submitted) to be more closely related to E. maximus (Leptostelma) than others of sect. Meridionales. The group of Juan Fernandez hexaploids segregated here as sect. Terranea probably are derived from sect. Meridionales.

19. Sect Microcephalum G.L. Nesom, sect. nov.

Habitu fibrosi-radicato non-rhizomato, caudice simplici, caulibus simplicibus, foliis basalibus in rosette, capitulis in alabastro erectis, radiis filiformibus arcte cincinatis distinctus. TYPE: Erigeron cuneifolius DC.

Annual to perennial, fibrous-rooted, not rhizomatous, stoloniferous in some; caudex simple; glabrous to sparsely strigose; stems simple, less commonly branched, filiform, bracteate; basal leaves in a rosette, spatulate with orbicular to obovate or cuneiform blades (oblanceolate-elliptic in E. purpuripes), 1-nerved, entire to shallowly crenate or serrate on the distal half, lobed to pinnatifid in some, cauline bracteate, subclasping or not clasping; heads 1(-few), tiny (involucres 2–6 mm long, 2–7(-8) mm wide), erect in bud; rays 24–54, 40–80(-100), white, filiform, tightly coiling; disc corollas 10–17, fewer than the ray; achenes 0.8–1.4 mm long, rectangular, 2-nerved (orange-resinous); pappus of 17–28 bristles.

E. bellidiastroides Griseb. (Cuba)

E. bellioides DC. (Puerto Rico, Cuba, or Hispaniola)

syn= E. semiovalis Urb. (Cuba)

E. capillipes Ekman & Urb. (Cuba)

E. cuneifolius DC. (Puerto Rico)

E. hyoseroides Griseb. (Cuba)

E. libanensis Urb. (Cuba)

E. ocoensis Urb. & Ekman (Hispaniola)

E. paucilobus Urb. (Cuba)

E. purpuripes Britton & P. Wilson (Cuba)

E. taylori Britton & P. Wilson (Cuba)

E. thrincioides Griseb. (Cuba)

E. vegaensis Urb. (Hispaniola)

These species were not fully accounted for in Nesom's (1989c) overview of Erigeron, except for the observation that the group, as characterized by E. cuneifolius and E. bellioides, probably belonged with sect. Cincinnactis. Erigeron bellioides shows as the sister taxon to Aphanostephus in the molecular analysis by Noyes (2000a). Erigeron cuneifolius has become a pantropical weed. The group is in need of revisionary study.

20. Sect. Olygotrichium Nutt., Trans. Amer. Philos. Soc. ser. 2, 7: 311. 1841. TYPE: Erigeron divergens Torr. & A. Gray

Heterochaeta DC., Prodr. 5: 282. 1836 (non Besser 1827). LECTOTYPE: Erigeron pubescens Knuth (Nesom, 1989c)

Erigeron [unranked sp. group] Bellidiastra Rydb., Fl. Colorado 359. 1906, in clave. TYPE: Erigeron bellidiastrum Nutt.

Erigeron [unranked sp. group] Divergentes Rydb., Fl. Colorado 359. 1906, in clave. TYPE: Erigeron divergens Torr. & A. Gray

Erigeron [unranked sp. group] Flagellares Rydb., Fl. Colorado 359. 1906, in clave. TYPE: Erigeron flagellaris A. Gray

Annual to biennial or perennial; taprooted or fibrous-rooted, not rhizomatous, sometimes producing runners or stoloniform branches; caudex usually simple; villous to hirsute to strigose or glabrate; stems simple or branched; leaves oblanceolate to obovate or spatulate, entire to toothed or lobed, not clasping (slightly subclasping in E. calcicola); heads nodding in bud; ray white to pink, often with an abaxial lilac midstripe, not coiling or reflexing; achenes (0.5-)0.7–1.6(-1.8) mm long, 2-nerved; pappus of 6–18(-19) bristles (16–25 in E. fundus, 23–30 in E. mihianus; bristles absent in E. onofrensis, E. versicolor).

Group A.

E. bellidiastrum Nutt.

E. bigelovii A. Gray

E. calcicola Greenm.

E. calvus Coville

E. divergens Torr. & A. Gray

E. flagellaris A. Gray

E. fundus G.L. Nesom

E. lemmonii A. Gray

E. metrius Blake

E. mihianus Blake

E. modestus A. Gray

E. multiceps Greene

E. onofrensis G.L. Nesom

E. pinkavii B.L. Turner

E. pubescens Kunth

E. religiosus Cronquist

E. sionis Cronquist (incl. E. proselyticus G.L. Nesom)

E. tracyi (syn = E. colomexicanus A. Nelson)

E. versicolor (Greenm.) Nesom (syn = E. gilensis Wooton & Standl.; syn = E. mimegletes Shinners)

E. vicinus G.L. Nesom

Group B.

E. lobatus A. Nelson

E. piscaticus G.L. Nesom

E. velutipes Hook. & Arn.

The three species of Group B (all taprooted annuals) are closely interrelated, apparently part of sect. Olygotrichium. They are characterized by a densely stipitateglandular and sparsely hispid-pilose vestiture with straight, spreading hairs 0.6–1.5 (-2) mm long. Their distinctions, with description of a new species, were discussed by Nesom (1989d). The report of E. velutipes in Arizona (Nesom and Baker, 1991) notes variability in habit, suggesting that a taxonomic review of this group would be useful.

Erigeron bigelovii should be investigated for possible affinities elsewhere, possibly with sect. Lamprocaules G.L. Nesom & R.D. Noyes. The short-hispid vestiture, wiry, brittle, highly branched stems, and involucral morphology are unusual in sect. Olygotrichium. Erigeron mihianus also is somewhat anomalous in sect. Olygotrichium, especially in its geography (Mt. Zempoaltepetl, Oaxaca) and high number of pappus bristles; on the other hand it produces leafy stolons and nonclasping, pinnatifid leaves.

21. Sect. Osteocaulis G.L. Nesom, Phytologia 67: 82. 1989. TYPE: Erigeron linearis (Hook.) Piper

Erigeron [unranked sp. group] Lutei Rydb., Fl. Rocky Mts. 897. 1918, in clave. TYPE: Erigeron luteus A. Nelson (=E. linearis)

Taprooted, perennial; caudex branched; stem vestiture of short, white, closely appressed hairs; stems simple or less commonly branched; leaves linear, entire, not clasping, leaf and stem bases white-indurate; heads erect (E. linearis) or nodding (E. bloomeri, E. elegantulus) in bud; rays coiling, yellow in E. linearis, absent in E. bloomeri; achenes (1.8-)3–4 mm long, 2-nerved; pappus of 10–50 bristles.

E. barbellatus Greene

E. bloomeri A. Gray

E. elegantulus Greene

E. linearis (Hook.) Piper

Molecular data (Noyes, 2000a) suggest that sect. Osteocaulis, sect. Spathifolium, and sect. Arenarioides may be closely interrelated. Species of sect. Arenarioides have white and highly sclerified leaf bases similar to those of sect. Osteocaulis. All have similar vestiture, as also does sect. Wyomingia.

22. Sect. Pauciflori G. Don in Loudon, Hort. Brit. 343. 1830. LECTOTYPE (Nesom 1989c): Erigeron bellidifolius Willd. (= Erigeron pulchellus Michx.)

Musteron Raf., Fl. Tellur. 2: 50. 1836. TYPE: “Erigeron bellidifolium” Raf. (probably = E. bellidifolius Willd. = E. puchellus Michx.)

Erigeron [unranked sp. group] Pulchelli Small, Man. Southeastern Fl. 1395. 1933, in clave. TYPE: Erigeron pulchellus Michx.

Perennial, rhizomatous, fibrous-rooted, primary rhizomes relatively slender, producing slender, herbaceous, scale-leaved, stoloniform rhizomes; caudex simple; villous; stems branched; leaves oblanceolate, toothed, clasping; heads nodding in bud; rays white, coiling tardily at tips; achenes 1.3–1.8 mm long, 2(-4)-nerved; pappus of (22-)28–36 bristles.

E. pulchellus Michx.

Erigeron pulchellus was earlier placed within sect. Fruticosus (see commentary in Nesom, 1989c) and the molecular analysis by Noyes shows it in an unresolved position close to species of that section. In view of its distinctive morphology and isolated geography, however, it seems reasonable to recognize the monotypic sect. Pauciflori, especially since it is not clear that sect. Fruticosus, as delimited here, is monophyletic.

23. Sect. Phalacroloma (Cass.) Torr. & A. Gray, Fl. N. Amer. 2(1): 175. 1841. Phalacroloma Cass., Dict. Sci. Nat. 39: 404. 1826. TYPE: Erigeron strigosus Muhlenb. ex Willd.

Diplemium Raf., Fl. Tellur. 2: 50. 1836. LECTOTYPE (Nesom, 1989c): Erigeron strigosus Muhlenb. ex Willd.

Erigeron [unranked sp. group] Ramosi Rydb., Fl. Colorado 359. 1906, in clave. TYPE: Erigeron ramosus (Walter) B.S.P. (= E. strigosus Muhlenb. ex Willd)

Erigeron [unranked sp. group] Annui Small, Man. Southeastern Fl. 1395. 1933, in clave. TYPE: E. annuus (L.) Pers.

Annual to biennial or short-lived perennial, fibrous-rooted, rhizomatous in some forms of E. strigosus; caudex simple; strigose to sparsely hirsute; stems branched; leaves oblanceolate, toothed, not clasping; heads loosely paniculiform or corymbiform, nodding in bud; rays white, not coiling or reflexing; achenes (0.5-)0.8–1.2 mm long, 2(-4)-nerved; pappus (disc florets) of 8–15 bristles, bristles absent (in E. annuus and E. strigosus) on ray florets.

E. annuus (L.) Pers.

E. strigosus Muhlenb. ex Willd.

E. tenuis Torr. & A. Gray

Sect. Phalacroloma has been restricted to two species that have pappose disc achenes but that lack the series of bristles on the ray achenes—Erigeron strigosus and E. annuus (Cronquist, 1947; Nesom, 1989c). Molecular data (Noyes, 2000a) place E. tenuis and E. strigosus as sister species, with E. annuus sister to this pair. Occasional plants are encountered that suggest hybridization occurs between E. tenuis and E. strigosus.

The reproductive biology and evolution of Erigeron strigosus and E. annuus are undergoing detailed study (Noyes and Rieseberg, 2000; Noyes, 2000b; Noyes, 2005; Noyes and Allison, 2005; Noyes, 2006a, 2006b; Noyes et al. 2007). Formal variants have recently been described at varietal rank within E. strigosus (Allison and Stevens, 2001; Noyes et al., 2006).

24. Sect. Polyactis (Less.) G.L. Nesom, Phytologia 66: 416. 1989. Polyactis Less., Syn. gen. Comp. 188. 1832. TYPE: Erigeron delphinifolius Willd.

Stenactis Cass., Dict. Sci. Nat. 37: 485. 1825 (non Erigeron sect. Stenactis Torr. & A. Gray). TYPE: Erigeron delphinifolius Willd.

Polyactidium DC., Prodr. 5: 281. 1836. TYPE: Erigeron delphinifolius Willd.

Achaetogeron A. Gray, Mem. Amer. Acad. Arts, n. ser. 4 (Pl. Fendl.): 72. 1849..

TYPE: Erigeron wislizeni (A. Gray) Greene

Perennial and fibrous-rooted or taprooted and annual; caudex simple or rarely branched, rhizomatous in some species; hirsute to strigose; stems branched, less commonly simple; leaves mostly oblanceolate to oblong, toothed or lobed to pinnatifid, less commonly entire, clasping or not clasping; heads usually in loosely corymbiform to paniculiform arrays, solitary in a few species, arching-nodding in bud; rays white to blue, filiform, reflexing; achenes 1–1.3 mm long, 2–4-nerved; pappus bristles 8–12 (to 17 in E. podophyllus), basally caducous, absent or greatly reduced in some species.

E. annuactis G.L. Nesom

E. basaseachensis G.L. Nesom

E. caulinifolius G.L. Nesom

E. circulis G.L. Nesom

E. coroniglandifer G.L. Nesom

E. dactyloides (Greenm.) G.L. Nesom

E. delphinifolius Willd.

E. eruptens G.L. Nesom

E. griseus (Greenm.) G.L. Nesom

E. inoptatus A. Gray

E. jenkinsii G.L. Nesom

E. mayoensis G.L. Nesom

E. nacoriensis G.L. Nesom

E. neomexicanus A. Gray

E. oreophilus Greenm.

E. podophyllus G.L. Nesom

E. polycephalus (Larsen) G.L. Nesom

E. rhizomactis G.L. Nesom

E. seemannii (Schultz-Bip.) Greene

E. subacaulis (McVaugh) G.L. Nesom

E. wislizeni (A. Gray) Greene

Two species have been described since the published revision of this section (Nesom, 1989a): E. jenkinsii (Nesom, 1993a) and E. mayoensis (Nesom, 1993b).

25. Sect. Pseuderigeron Torr. & A. Gray, Fl. N. Amer. 2(1): 177. 1841. LECTOTYPE: Erigeron caespitosus Nutt. (Nesom, 1989c)

Erigeron [unranked sp. group] Caespitosi Rydb., Fl. Colorado 359. 1906, in clave. TYPE: Erigeron caespitosus Nutt.

Perennial, taprooted; caudex branches relatively thick and short, retaining old leaf bases; stems simple, erect to decumbentascending; stems and leaves eglandular, involucres glandular or eglandular; leaves basal (persistent) and cauline, narrowly oblanceolate to spatulate (1-)3-nerved, cauline gradually reduced, not clasping; heads 1–4, erect? in bud; rays white to blue, coiling, often weakly; achenes 1.5–2.2 mm long, 2-nerved; pappus of 12–25 bristles.

E. abajoensis Cronquist

E. caespitosus Nutt.

E. goodrichii S.L. Welsh

Erigeron abajoensis is a segregate of E. caespitosus, separated from the latter only by its strigose (versus hirsute) stems and leaves and greater tendency for 1-nerved leaves.

26. Sect. Pycnophyllum Cronquist, Brittonia 6: 141. 1947. TYPE: Erigeron foliosus Nutt.

Perennial, taprooted; short caudexlike branches or relatively slender, rhizomelike caudex branches producing numerous, basally ascending stems, sometimes with slender, lignescent offsets; hirsute to strigose, puberulous, or glabrous; stems fewbranched, rarely simple; leaves filiform to linear-oblanceolate, entire, not clasping; heads 1 or 2–5(-10) in loosely corymbiform arrays, erect in bud; rays white to blue, weakly coiling, sometime only at the tips, sometimes apparently not coiling, absent in some species; achenes 1.8–3 mm long, 2–4 (-5)-nerved; pappus of 17–45(-61 in E. reductus) bristles.

E. aequifolius Hall

E. angustatus Greene

E. biolettii Greene

E. blochmaniae Greene

E. breweri A. Gray

E. elmeri (Greene) Greene

E. foliosus Nutt.

E. inornatus A. Gray

E. klamathensis (G.L. Nesom) G.L. Nesom

E. mariposanus Congdon

E. miser A. Gray

E. oxyphyllus Greene

E. petrophilus Greene

E. reductus (Cronquist) G.L. Nesom

E. sanctarum S. Watson

E. serpentinus G.L. Nesom

E. supplex A. Gray

This group (as sect. Linearifolii) was revised by Nesom (1992a), bringing a number of changes in circumscriptions of taxa; one new species, E. serpentinus, was added. Erigeron klamathensis was raised in rank (Nesom, 2004). Erigeron hyssopifolius was excluded by Nesom and Noyes (1999) to constitute the monotypic sect. Linearifolii. Erigeron supplex and E. sanctarum are placed here in sect. Pycnophyllum for the first time, although Cronquist (1947) earlier noted the resemblance of E. supplex to this group of species and to a putative close relationship between E. supplex and E. sanctarum. Sect. Pycnophyllum is centered in California, extending northward to Washington and southward into Baja California; E. oxyphyllus is the southeasternmost species, occuring in Sonora and Arizona.

27. Sect. Quercifolium G.L. Nesom, sect. nov.

Duratione annuo vel breviviventi, caudice simplici, foliis serratis vel lobatis amplexicaulibus vel subamplexicaulibus, vestimento caulino deflexo, et radii noncincinatis distinctus. TYPE: Erigeron quercifolius Lam.

Erigeron [unranked sp. group] Philadelphici Rydb., Fl. Colorado 359. 1906, in clave (non Small 1933). TYPE: Erigeron philadelphicus L.

Annual or short-lived perennial, fibrous-rooted, taprooted in E. geiseri, E. tenellus, E. turnerorum, stoloniferous in E. basilobatus, E. cieloensis, E. domingensis, E. polycladus, E. psilocaulis, rhizomatous in E. dryophyllus, E. veracruzensis; caudex simple; strigose-pilose to hirsute, often deflexed on the proximal portions of stem; stems branched; leaves oblanceolate, to elliptic, entire or crenately toothed to pinnately lobed, cauline clasping to subclasping or not; heads 1 or 2–35(-50) in diffuse arrays from distal branches, nodding or archingnodding in bud; rays not coiling or reflexing, white to blue; achenes 0.6–1.8 mm long, 2-nerved; pappus of 8–32 bristles.

North American

E. basilobatus Blake (ne Mexico)

E. cieloensis G.L. Nesom (ne Mexico)

E. dryophyllus A. Gray (ne Mexico)

E. geiseri Shinners (central Texas and s Oklahoma)

E. heleniae G.L. Nesom (ne Mexico)

E. philadelphicus L. (e USA)

E. quercifolius Lam. (e USA)

E. tenellus DC. (ne Mexico, s Texas)

E. turnerorum G.L. Nesom (ne Mexico)

E. veracruzensis G.L. Nesom (ne Mexico) Caribbean

E. caeruleus Urb. (Hispaniola)

E. darrellianus Hemsl. (Bermuda)

E. dissectus Urb. (Hispaniola)

E. domingensis Urb. (Hispaniola)

E. fuertesii Urb. (Hispaniola)

E. jamaicensis L. (Jamaica)

syn= E. earlei Britton & P. Wilson (Cuba)

syn= E. polycladus Urb. (Martinique)

syn= E. rivularis Sw. (Jamaica, Hispaniola)

E. pinetorum Urb. (Hispaniola) (= E. buchii Urban?)

E. polycladus Urb. (Martinique)

E. psilocaulis Urb. (Hispaniola)

Some species of this group (Erigeron quercifolius, E. philadelphicus, E. caeruleus, E. dryophyllus, E. turnerorum, and E. tenellus) were placed by Nesom (1989c) within sect. Olygotrichium, while another related group (including E. darrellianus, E. jamaicensis, and others) was noted as probably belonging in the same section. A new species was described (Nesom, 1989e)—E. cieloensis, putatively the sister species of E. basilobatus, which is transferred here from sect. Cincinnactis (sensu Nesom, 1989c). Erigeron heleniae is recently described (Nesom, 2007). Molecular data of Noyes (2000a) indicate that sect. Quercifolium is phyletically coordinate with the clade that includes Aphanostephus and Erigeron sect. Microcephalum.

Sect. Quercifolium, as delimited here, is the only section of Erigeron with a distribution divided between the Caribbean, Mexico, and the United States. The Caribbean species (type localities in parenthesis) are closely similar to E. quercifolius: E. caeruleus, E. dissectus, E. fuertesii (perhaps conspecific with E. caeruleus), and E. jamaicensis. Erigeron darrellianus apparently is the only Northern Hemisphere species of the genus to have developed a distinctly shrubby habit. Erigeron domingensis is remarkably similar in habit to E. flagellaris (of sect. Olygotrichium, with herbaceous stolons, tendency for a single head on the erect stems), but E. domingensis has more herbaceous phyllaries, white to blue or purple rays without an abaxial midstripe, and up to 3 capitula per stem, probably derived from its relatives with a corymbiform capitulescence.

Erigeron tenuis, previously regarded as closely related to E. geiseri (Nesom, 1987, 1989e), is placed in the present treatment with sect. Phalacroloma. Erigeron pinetorum Urb. was previously placed as a close relative of the species related to E. quercifolius but is now known to be conspecific with Conyza primulifolia (Lam.) Cuatrec. & Lourteig (= Conyza chilensis Spreng.).

28. Sect. Radicati (Rydb.) Nesom, comb. et stat. nov.

Erigeron [unranked sp. group] Radicati Rydb., Fl. Colorado 359. 1906, in clave. TYPE: Erigeron radicatus Hook.

Erigeron [unranked sp. group] Laetevirentes Rydb., Fl. Rocky Mts. 897. 1918, in clave. TYPE: Erigeron laetevirens Rydb. (= E. ochroleucus)

Perennial, taprooted; caudex multicipital or with short, thick branches; hirsutulous to villosulous, hairs with purplish cross walls (except in E. rydbergii); stems simple, less commonly branched; leaves oblanceolate to spatulate, entire, not clasping, abaxial faces glabrous or glabrate, adaxial faces strigose to villous (both faces hairy in E. parryi); heads 1(-3), behavior in bud not known, phyllaries minutely glandular; rays coiling (not coiling in E. parryi); achenes 1.8–2.8 mm, 2-nerved; pappus of 12–20 bristles (caducous in E. parryi, E. radicatus).

E. lackschewitzii G.L. Nesom & Weber

E. ochroleucus Nutt. (incl. E. scribneri Canby ex Rydb.)

E. parryi Canby & Rose

E. radicatus Hook. (incl. E. huberi S.L. Welsh & N.D. Atwood)

E. rydbergii Cronquist

Erigeron parryi differs from the other species in its apparently non-coiling rays and leaves equally strigose to hirsute-strigose on both faces; like most of the others, however, it produces hairs with purplish cross walls and the pappus bristles are basally caducous, as also in E. radicatus (Nesom, 2004). This group was placed in sect. Asteroidea in 1989 as the “E. radicatus group.”

29. Sect. Rhizonexus G.L. Nesom, sect. nov.

Distinctus habitu fibrosi-radicato rhizomato, caudex systemata diffusa ramorum tenuium rhizomiformium formans. TYPE: Erigeron ursinus D. Eaton

Perennial, rhizomatous, fibrous-rooted, forming diffuse systems of slender, rhizomelike caudex branches; glabrous or sparsely strigose; stems simple or few-branched; leaves narrowly oblanceolate to oblong, entire, not clasping; heads 1(-3), erect in bud; rays blue to pink or purple, not reflexing or coiling or sometimes coiling slightly at the tips; achenes 1.5–2 mm long, 2-nerved; pappus of 10–21 bristles.

E. gracilis Rydb.

E. ursinus D. Eaton

The morphological similarity of Erigeron gracilis and E. ursinus and their apparent morphological isolation as a group were noted by Cronquist (1947) and by Nesom (1989c), where they were treated as the “E. ursinus group” of sect. Asteroidea. Erigeron leiomerus (treated here within sect. Asterigeron) was placed by molecular data (Noyes, 2000a) in a sister relationship to E. ursinus, but E. gracilis was not included in the molecular sampling.

30. Sect. Scopulincola Nesom, Phytologia 67: 84. 1989. TYPE: Erigeron scopulinus G.L. Nesom & Roth

Perennial, taprooted; caudex branches long, slender, rhizomelike; glabrous or nearly so; stems simple or branched; leaves oblanceolate to obovate or spatulate, entire or pinnatisect in some, folding along the midvein, not clasping; heads 1–4, nodding in bud, phyllaries graduate and densely glandular but otherwise glabrous to sparsely strigose, often purplish; rays white, reflexing (absent in E. mancus); achenes 1.2–2.3 mm long, 2-nerved; pappus of 11–30 bristles.

Group A. Leaves spatulate, entire; Arizona, New Mexico, Colorado, Utah, Nevada, Montana, Wyoming.

E. kachinensis S.L. Welsh & Moore

E. leiomerus A. Gray

E. nauseosus (M.E. Jones) A. Nelson

E. scopulinus Nesom & Roth

Group B. Leaves mostly toothed to pinnatifid; Arizona.

E. anchana G.L. Nesom

E. heliographis G.L. Nesom

E. pringlei A. Gray

E. saxatilis G.L. Nesom

Group C. Leaves pinnatisect; high elevation in New Mexico, Colorado, Utah, Wyoming.

E. mancus Rydb.

E. pinnatisectus (A. Gray) A. Nelson

Sect. Scopulincola (especially Group A) is distinguished from sect. Asterigeron primarily on the basis of the reflexing ray behavior. The toothed to pinnatifid leaves of Groups B and C are a further distinction. A recent study of the Erigeron. pringlei group (Nesom, 1990b) resulted in the description of three additional species related to E. pringlei, all separated here as Group B.

The Noyes analysis (2000a) suggests that E. pinnatisectus is closely related to sect. Scopulincola, where its pinnatifid leaves are similar to those of E. pringlei, rather than to the 3-parted ones of sect. Tridactylia. Erigeron mancus, closely similar to E. pinnatisectus, is also transferred here from sect. Tridactylia. Both species also have folding leaves and reflexing rays like others of sect. Scopulincola.

31. Sect. Stenactis Torr. & A. Gray, Fl. N. Amer. 2(1): 172. 1841. LECTOTYPE (Nesom 1989c): Erigeron pumilus Nutt.

Erigeron [unranked sp. group] Pumili Rydb., Fl. Colorado 359. 1906, in clave. TYPE: Erigeron pumilus Nutt.

Perennial, taprooted; caudex branches not thickened, leaf bases not marcescent; petiole bases ciliate; heads commonly more than 1 per stem, nodding in bud; leaves linear-oblanceolate to narrowly oblanceolate or oblanceolate-spatulate, 1-nerved, cauline well-developed (except var. condensatus); rays reflexing (laminae reduced in E. aphanactis, E. calvus, E. concinnus; ray florets 0 in E. ovinus); disc corolla throat white-indurate and inflated (not inflated in E. pygmaeus); achenes 1.2–2 mm long (2.3–2.8 mm in E. pygmaeus); pappus bristles 7–27.

E. aphanactis (A. Gray) Greene

E. calvus Coville

E. clokeyi Cronquist

E. concinnus (Hook. & Arn.) Torr.& A.Gray

E. engelmannii A. Nelson

E. maguirei Cronquist

E. pumilus Nutt. (incl. E. zothecinus S.L. Welsh)

E. pygmaeus (A. Gray) Greene

E. vetensis Rydb.

This group was placed by Nesom (1989c) as the “Erigeron pumilus group” of sect. Asteroidea. It was later treated with other species with sharply reflexing rays as an informal subgroup within sect. Geniculactis (Nesom, 1990c). Molecular data, in contrast, indicate that the E. pumilus group is phylogenetically removed from sect. Geniculactis sensu stricto, and the distinctive morphology of the group suggests that it be separately and formally recognized. The species occur at low to mid-level elevations in the western U.S.A. Erigeron pygmaeus grows at higher elevations and is anomalous in several morphological features.

The narrow Utah endemic Erigeron maguirei fits within sect. Stenactis in features of habit as well as ray and bud behavior. Among the other species, it is most similar in its subspatulate leaves to the rare E. calvus from the Inyo Mountains of California.

The placement here of Erigeron ovinus emphasizes the tendency for reduction or loss of rays prevalent in the section. Bud behavior is not known, and the 3-nerved leaves and deflexed-hirsute cauline vestiture suggest that it may instead be related to E. caespitosus (sect. Asteroidea, Group B) (Blake first described E. ovinus as E. caespitosus var. anactis). It also is similar in some respects to E. nauseosus (sect. Scopulincola, Group A). Erigeron ovinus is endemic to the Sheep and Groom ranges and Mount Irish in Clark and Lincoln cos., Nevada

32. Sect. Terranea (Colla) Nesom, comb. et stat. nov.

Terranea Colla, Mem. Accad. Sci. Torino 38 (Pl. Rar. Chil., Fasc. 4): 11, t. 23. 1835 [reprints 1834]. TYPE: Terranea fernandeziana Colla

Perennial herbs to subshrubs or (Erigeron fernandezianus) woody shrubs or small trees, rhizomatous; caudex simple; glabrous to strigose; stems branched; leaves oblanceolate, to lanceolate, entire to toothed or pinnatifid, not clasping; heads 1 or in a loosely corymbiform array, erect in bud; rays, white, not coiling or reflexing; achenes 1–2 mm long, 2-nerved; pappus of [not counted] bristles. All species are hexaploid, 2n = 54 (Valdebenito et al. 1992).

E. ingae Skottsb.

E. luteoviridis Skottsb.

E. fernandezianus (Colla) Solbrig

E. rupicola Phil.

E. “stuessyi” (ined.)

E. turricola Skottsb.

Sect. Terranea comprises a group of six apparently closely related species endemic to the Juan Fernandez Islands of Chile and are hypothesized (based on an analysis of morphological, chromosomal, and flavonoid data) to have radiated from a single introduction to the island more distant from the mainland (Isla Masafuera; Valdebenito et al., 1992). The epithet “stuessyi” was applied to one of the species in the publication by Valdebenito et al. (1992), but the name has never been validated.

Among South American mainland species included in a survey for possible ancestors, the Valdebenito et al. (1992) study placed Erigeron leptorhizon DC. (2n = 18) (see Conyza group A = Erigeron sect. Caenotus) as the species most similar to the E. fernandezianus group, but the molecular analysis of Noyes (2000a) instead places E. fernandezianus as closely related to the other group of species commonly placed in Conyza (see Conyza group B), distantly related to E. leptorhizon. As noted by Valdebenito et al. (1992, p. 477), “Continental species with a chromosome number of n = 27 would be more probable as an ancestral taxon.” Plants of the mainland species E. ecuadoriensis and E. lanceolatus (see sect. Meridionales) are known to be hexaploid, and it seems likely that the Juan Fernandez endemics are derived from sect. Meridionales.

The Noyes (2000a) molecular analysis included two samples of Erigeron rosulatus: the mainland sample is closely related to other mainland species (here in sect. Meridionales), while the sample from the Juan Fernandez Islands clusters with the species of sect. Terranea.

33. Sect. Tridactylia Nutt., Trans. Amer. Philos. Soc. ser. 2, 7: 310. 1841. TYPE: Erigeron compositus Pursh.

Erigeron series Multifidi Rydb. ex J.F. Macbr. & Payson, Contr. Gray Herb. 49: 73. 1917. Erigeron [unranked sp. group] Multifidi Rydb., Fl. Colorado 359. 1906, in clave. LECTOTYPE: Erigeron compositus Pursh. (Nesom, 1989c)

Erigeron [unranked sp. group] Compositi Rydb., Fl. Rocky Mts. 896. 1918, in clave. TYPE: Erigeron compositus Pursh.

Taprooted, perennial; caudex divided into slender, rhizomelike branches (variable in Erigeron compositus); glabrous to strigose or hispid; stems simple (few-branched in E. basalticus and E. allocotus); leaves oblanceolate to spatulate 3-lobed or 3-toothed near the apex, not clasping; heads erect in bud; rays white, weakly coiling or not at all (sometimes distinctly in E. compositus); achenes 1.5–2.7 mm long (3.5–4 mm in E. lanatus), 2-nerved; pappus of 10–20 bristles (25–35 in E. lanatus).

E. allocotus Blake

E. basalticus Hoover

E. compositus Pursh

E. denalii A. Nelson (incl. E. mexiae K. Becker)

E. flabellifolius Rydb.

E. lanatus Hook.

E. pallens Cronquist

E. purpuratus Greene

E. salishii Douglas & Packer

E. trifidus Hook.

E. vagus Payson

Recent studies have explored the nature of variation in sexual and agamospermic populations of E. compositus (Noyes and Soltis, 1996; Noyes et al., 1995). Erigeron pinnatisectus was shown by Noyes (2000a) to be distantly related to sect. Tridactylia; E. pinnatisectus and its close relative E. mancus, both of which have pinnately dissected leaves (vs 3-lobed or 3-toothed), are here transferred to sect. Scopulincola.

A possible relationship of Erigeron lanatus to sect. Erigeron needs to be investigated; the leaves are entire or weakly 3-toothed at the apex, and the species was speculated to be involved as a parent in the hybrid origin of E. trifidus (Packer, 1983). The origin of E. trifidus through hybridization between E. lanatus and E. compositus was confirmed by Burke (2005), although as currently recognized, E. trifidus probably is polyphyletic. An ambiguous, slender taprootlike structure sometimes is observed in E. lanatus at the base of the caudex, but this may be a rhizome; the diffuse system of relatively long, slender, rhizomelike, branches is similar to morphology in sect. Tridactylia.

34. Sect. Trimorpha (Cass.) DC., Prodr. 5: 290. 1836. Trimorpha Cass., Bull. Sci. Soc. Philom. Paris 1817: 137. 1817. Erigeron subg. Trimorpha (Cass.) Popov, Acta Inst. Bot. Acad. Sci. URSS, Ser. 1, Fasc. 7: 10. 1948. TYPE: Erigeron acris L.

Trimorpha sect. Brachyglossae Vierh., Beih. Bot. Centralbl. 19: 423. 1906. Erigeron subsect. Brachyglossae (Vierh.) Pawlowski, Fragm. Florist. Geobot. 16: 256. 1970. Lectotype(Nesom, 1989b): Erigeron acris L.

Trimorpha sect. Macroglossae Vierh., Beih. Bot. Centralbl. 19: 424. 1906. Lectotype (Nesom, 1989b): Erigeron alpinus L.

Tessenia P. Bubani, Fl. Pyrenaea 2: 264. 1899. Lectotype: Erigeron alpinus L. (Nesom, 1989b)

Erigeron [unranked sp. group] Acres Rydb., Fl. Colorado 359. 1906, in clave. TYPE: Erigeron acris L.

Fibrous-rooted, perennial, biennial, or annual; caudex usually simple; stems usually branched; leaves mostly entire, not clasping; heads erect in bud, in a corymbiform to broadly racemiform cluster; inner involucral bracts long-attenuate to caudate; ray (pistillate) florets in 2 zones, those of the outer zone with erect, filiform, white to pink or purplish lamina, not coiling or reflexing, those of inner zone without lamina; achenes 2–2.4 mm long, 2-nerved; pappus bristles 12–35, accrescent (elongating in fruit to ca. 2 times involucres).

E. acris L. * (incl. E. kamtschaticus DC.,

E. angulosus Gaudichaud*, E. droebachiensis O.F. Müll.*, E. elongatus Ledeb., and E. politus Fries*)

E. alpinus L.*

E. atticus Villars*

E. baicalensis Botsch.

E. borealis (Vierh.) Simmons*

E. canariensis O. Sida

E. caucasicus Steven*

E. cyanactis Rech. f.

E. elatus Hook.

E. epiroticus (Vierh.) Halácsy*

E. glabratus Hoppe & Hornsch. ex Bluff & Fingerh.*

E. granatensis Lippert

E. hispanicus (Vierh.) Maire

E. lalehzaricus (Rech.) O. Sida

E. leptocladus Rech. f.

E. macrophyllus Herbich

E. mesatlanticus Maire

E. nannogeron Rech. f.

E. neglectus Kerner*

E. nivalis Nutt. (= E. debilis (A. Gray) Rydb.; E. scotteri Boivin)

E. orientalis Boiss.

E. podolicus Besser

E. pseudoelongatus Botsch.

E. semibarbatus DC.

E. serotinus Weihe

E. uralensis Less.

E. venustus Botsch.*

(*asterisks denote Eurasiatic species studied by Huber and Nilsson, 1995)

Nesom (1989b) hypothesized that sect. Trimorpha (as the genus Trimorpha) is separate from Erigeron, more closely related to Conyza, and provided nomenclatural transfers for North American taxa. Studies by Walter Huber and colleagues and by Noyes (2000a), however, have made it clear that species of sect. Trimorpha are closely related to those of sect. Erigeron and that both sections are relatively recently derived within the genus (Huber, 1993; Huber and Leuchtmann, 1992; Huber and Nilsson, 1995; Huber and Zhang, 1991; Oberhänsli and Huber, 1993; Utelli et al., 1995).

The North American species are Erigeron acris (circumboreal), E. elatus, and E. nivalis. The Eurasiatic species are diploids with identical karyotypes and their high genetic identities suggest very recent evolutionary differentiation. Some of these are among nine species listed by Sida (1988) as “Species excludendae”—he gave no comment about the reason for their exclusion or their suggested disposition: E. alpinus, E. atticus, E. borealis, E. epiroticus, E. gaudinii Brügger, E. hungaricus (Vierh.) Pawl., E. neglectus, E. orientalis Boiss., and E. rhodopaeus (Vierh.) Hayek.

Sida (1988) formally divided sect. Trimorpha into three series, based primarily on form of the capitulescence and vestiture: ser. Trimorpha O. Sida, ser. Politae O. Sida, and ser. Macrophyllae O. Sida.

As suggested by Nesom (1994c) and as discussed in detail and experimentally confirmed by Huber and Nilsson (1995) and Noyes (2000a), autogamous breeding systems apparently have arisen independently in a number of Astereaean groups, including Trimorpha and Conyza. In these, the pistillate florets of a head are greatly increased in number (often outnumbering the bisexual florets), in several series, the inner sometimes reduced to filiform eligulate florets, and the outer with reduced lamina.

35. Sect. Wyomingia (A. Nelson) Cronquist, Brittonia 6: 140. 1947.

Wyomingia A. Nelson, Bull. Torrey Bot. Club 26: 249. 1899. TYPE: Erigeron pulcherrimus A.A. Heller

Erigeron [unranked sp. group] Cani Rydb., Fl. Colorado 359. 1906, in clave. TYPE: Erigeron canus A. Gray

Erigeron [unranked sp. group] Tetrapleuri Rydb., Fl. Rocky Mts. 897. 1918, in clave. TYPE: Erigeron tetrapleuris (A. Gray) Heller (= E. utahensis)

Taprooted; perennial; caudex simple or with short, thick branches; vestiture strigillose of short, closely appressed hairs; stems simple or branched; leaves linear to narrowly oblanceolate, not clasping; heads erect in bud (nodding? in Erigeron compactus); rays white to blue, coiling (reflexing in E. canus, E parishii); achenes (1.5-)2-3.4 mm long, 2-nerved, (2-)4(-6)-nerved, or 6–8-nerved, (8-)10–14-nerved (E. canus), strigose to strigose-sericeous or with velutinous-ciliate margins and glabrous faces; pappus of 15–50 bristles (9–10 in E. katiae).

Group A. Stems branched; cauline leaves prominent; heads numerous, erect in bud; rays coiling; achenes (2-)4(-6)-nerved, sparsely strigose.

E. sparsifolius Eastw.

E. utahensis A. Gray

Group B. Stems simple, heads 1; leaves mostly basal and linear, cauline reduced; heads 1; achenes 2-nerved, faces glabrous, margins pilose-sericeous.

E. compactus Blake

E. consimilis Cronquist

E. sivinskii G.L. Nesom

Group C. Stems simple or branched, heads 1–4; leaves basal and cauline; achenes 2-nerved, villous-hirsute; pappus of 9–10 (E. katiae) or 15–25 (E. nematophyllus) bristles.

E. katiae N.D. Atwood and S.L. Welsh (2007)

E. nematophyllus Rydb.

Group D. Stems simple; leaves mostly basal and linear, cauline reduced; heads 1; achenes 2-nerved (Erigeron untermannii) or 4–8-nerved, faces strigose-sericeous.

E. argentatus A. Gray

E. pulcherrimus A.A. Heller (incl. E. bistiensis G.L. Nesom & Hevron)

E. untermannii S.L. Welsh (incl. E. carringtonae S.L. Welsh)

Group E. Stems simple or branched; leaves linear, mostly basal (Erigeron canus) or basal and cauline (E. parishii); heads 1–4 (E. canus) or 1–5(-10) (E. parishii), nodding in bud; rays reflexing (also slightly coiling at tips in E. parishii); achenes (8-)10–14-nerved, terete, glabrous (E. canus) or 4-nerved, angled, sparsely strigose to pilose (E. parishii).

E. canus A. Gray

E. parishii A. Gray

Sect. Wyomingia, as outlined here, is a heterogeneous group united by strigillose vestiture, linear leaves, and coiling rays (except in Group E). Achenes tend to be multi-nerved in Groups A and E and densely hairy in Groups B, C, and D. The leaves of Erigeron untermannii are often spatulate and glabrous to glabrate abaxially, features more similar to E. radicatus and its close relatives; rays of E. untermannii apparently tend to both coil and reflex. The two species of Group E are unique in their combination of nodding heads and reflexing rays. Problems in discerning relationships among the subgroups also were pointed out in the original description of E. sivinskii (Nesom, 1991).

Studies by Tonne (1999) indicate that Erigeron bistiensis is a synonym of E. pulcherrimus and support the hypothesis (Nesom and Hevron, 1995) that E. untermannii and E. carringtonae are conspecific. Neel and Ellstrand (2001) studied patterns of allozyme diversity in E. parishii, which is threatened by mining. Distinctions between E. utahensis and E. sparsifolius were noted by Nesom (2004).

Aphanostephus DC., Prodr. 5: 310. 1836. Type: Aphanostephus ramosissimus DC.

Keerlia DC., Prodr. 5: 309. 1836. Lectotype (designated here): Keerlia ramosa DC. = Aphanostephus ramosissimus var. ramosus (DC.) B.L. Turner & Birdsong

Leucopsidium Charpentier ex DC., Prodr. 6: 43. 1838. Type: Leucopsidium arkansanum DC. = Aphanostephus skirrhobasis (DC.) Trel.

Aphanostephus subg. Euaphanostephus Blake, Contr. Gray Herb. 53: 24. 1918. Type: A. ramosissimus DC.

Aphanostephus subg. Pappophanus Blake, Contr. Gray Herb. 53: 24. 1918. Type: A. skirrhobasis var. hallii (A. Gray) Blake

Aphanostephus sect. Pappophanus (Blake) Shinners, Wrightia 1: 101. 1946.

Aphanostephus sect. Pappopecus Shinners, Wrightia 1: 108. 1946. Lectotype: A. ramosissimus DC. (designated here)

Annual or perennial, taprooted; caudex simple, stems branched; leaves oblanceolate, slightly clasping or not clasping; heads nodding in bud; rays with abaxial midstripe, not coiling or reflexing; achenes thickribbed, columnar, 4-angled, often bearing duplex trichomes with a coiled or recurved apex; pappus a low, fimbriate- or ciliaterimmed corona (in A. skirrhobasis var. kidderi (Blake) B.L. Turner, the pappus members may appear as relatively slender, barbellate bristles with expanded bases). The genus is distinguished by its combination of ovate-lanceolate, thin-margined phyllaries, conical receptacles, achene morphology, pappus, and base chromosome number of x = 5.

A. pilosus Buckley

A. ramosissimus DC. (incl. A. arizonicus

A. Gray, A. humilis (Benth.) A. Gray, A. jaliscensis Shinners, A. pachyrrhizus Shinners, A. potosinus Shinners, and A. ramosus (DC.) A. Gray)

A. riddellii Torr. & A. Gray

A. skirrhobasis (DC.) Trel. (incl. A. kidderi Blake)

Aphanostephus includes four species (including eight varietal taxa) restricted to the south-central USA and the northern half of Mexico, as recognized by Turner (1984). Turner's phylogenetic reconstruction of the genus, based on morphology, was largely corroborated by Elisens et al. (1992)

Compared to Aphanostephus, other species of Conyzinae are conservative in involucral morphology (phyllaries linear-lanceolate, without wide, thin-scarious margins), achene morphology and vestiture (thin-walled, flat, mostly 2-nerved but subterete and multinerved in a few taxa, the duplex hairs never glochidiate), pappus (of barbellate bristles or reduced), and base chromosome number (x= 9) (see Nesom, 2000a). The genus was hypothesized to be closely related to Townsendia, Astranthium, and a group of Southern Hemisphere genera (subtribe Brachyscominae) on the basis of morphological features (Nesom, 1994d). In contrast, molecular data (cf. Morgan, 1990; Noyes, 2000a; Noyes and Rieseberg, 1999) indicate that Aphanostephus has arisen from within the Conyzinae, apparently closely related to sect.Microcephalumand sect. Cincinnactis.

Apopyros Nesom, Phytologia 76: 177. 1994. TYPE: Apopyros warmingii (Baker) G.L. Nesom

Perennial, from a thick, ligneous, sometimes tuberous rhizome; caudex simple; glabrate to sparsely pilose-hirsute; stems simple or branched; leaves all cauline, the proximal scalelike, linear-lanceolate to elliptic above, with 3 parallel nerves, entire, not clasping; heads 1–4 or 15–75 in a thyrsoid-cormbiform arrangement, erect in bud; rays absent (peripheral florets pistillate, fertile, tubular with 3–4 apical teeth); achenes 1.8–4 mm long, subcylindric, with (4-)5(-6) orange-resinous nerves; pappus of 28–40 bristles.

A. corymbosus (Hook. & Arn.) Nesom

A. warmingii (Baker) Nesom

Apopyros includes two species mostly in Brazil but reaching Paraguay and northeastern Argentina. Nesom (1994c) observed that Apopyros is similar to Neja in its parallelveined leaves with shiny-indurate surfaces, multinerved and nearly terete achenes, and tendency to produce stiffly pilose-hirsute vestiture, but Noyes (2000a) found that Apopyros is more closely related to Leptostelma.

Conyza [group A]

Erigeron sect. Caenotus Nutt., Gen. Plant. 2: 148. 1818. Conyza sect. Caenotus (Nutt.) Cronquist ex Cuatrec., Webbia 24: 211. 1969. TYPE: Erigeron canadensis L.

Conyzella Fabr., Enum. (ed. 1) 86. 1759. TYPE: Erigeron canadensis L.

Leptilon Raf., Amer. Monthly Mag. 268. 1818. TYPE: Erigeron divaricatus Michx.

Erigeron sect. Multiflori G. Don in Loudon, Hort. Brit. 343. 1830. Lectotype (Nesom 1989c): Erigeron canadensis L.

Suffrutescent perennial (Erigeron crenatus, E. socorrensis) or annual; taprooted; caudex simple; hirsute to nearly glabrous; stems branched; leaves linear to lanceolate or oblanceolate, entire or toothed, not clasping; heads erect in bud, in a columnar to pyramidal or loosely corymbiform arrangement; rays white, filiform, lamina slightly longer than the involucre, not coiling (apparently coiling in E. socorrensis) or reflexing; achenes 0.8–1.5 mm long, 2-nerved; pappus of 11–20 bristles.

Erigeron canadensis L. (= Conyza canadensis (L.) Cronquist)

Erigeron crenatus Eastw.

Erigeron divaricatus Michx. (= Conyza ramosissima Cronquist)

Erigeron leptorhizon DC. (= E. gaudi chaudii DC.)

Erigeron socorrensis I.M. Johnston

Erigeron subalpinus Urb.

Variation in Erigeron crenatus and E. socorrensis, from Isla Socorro of the Revillagigedo Islands, Mexico, was studied by Nesom (1990h). Erigeron subalpinus is endemic to Cuba and was described as very similar to Erigeron canadensis.

Conyza [group B]

Conyza Less., Syn. Gen. Comp. 203. 1832. Erigeron sect. Conyza (Less.) Baill., Hist. Pl. 8: 143. 1882. TYPE: Conyza chilensis (Spreng.) d. Don ex D. Don = Conyza primulifolia Lourteig & Cuatrec.

Astradelphus E.J. Remy [nom. nov.], Ann. Sci. Nat. Bot. ser. 3, 12: 185. 1849. Gusmania E.J. Remy in C.Gay,Hist. Chile Bot. [Fl. Chilena] 4: 12. 1849 (non Guzmania Ruiz & Pavon 1802). TYPE: Astradelphus chilensis (Spreng.) E.J. Remy = Gusmania chilensis (Spreng.) E.J. Remy = Conyza chilensis Spreng. = Conyza primulifolia (Lam.) Cuatrec. & Lourteig= Erigeron chilensis (Sprengel) D. Don ex G. Don in Loudon = Erigeron remyanus Wedd.

Annual to perennial; taprooted; caudex simple; hirsute to strigose, often strongly glandular; stems simple or branched; leaves lanceolate to oblanceolate or spatulate, entire to toothed or lobed, clasping or not clasping; heads erect in bud; rays white, lamina absent to slightly longer than the involucre; achenes 0.8–2 mm long, 2-nerved; pappus of ca. 10–25 bristles.

Conyza arabidifolia E.J. Remy

Erigeron bonariensis L. (= Conyza bonariensis (L.) Cronquist)

Conyza burkartii Zardini

Erigeron chilensis (Spreng.) D. Don ex G. Don in Loudon (= Conyza primulifolia (Lam.) Lourteig & Cuatrec. = Conyza chilensis Spreng.)

Conyza deserticola Phil.

Erigeron floribundus (Kunth) Schultz-Bip. (= Conyza floribunda Kunth)

Erigeron laevigatus Rich. (= Conyza laevigata (Rich.) Pruski = Conyza apurensis Kunth)

Conyza microcephala Hemsl.

Erigeron pazensis Schultz-Bip. ex Rusby Erigeron pinnatus Turcz. 1851 (non L. 1753) (= Conyza cardaminifolia Kunth; E. cardaminifolia (Kunth) Wedd.; E. turczaninowii Wedd.)

Erigeron spiciformis Griseb. (= Conyza spiciformis (Griseb.) Zardini)

Erigeron spiculosus Hook. & Arn. (= Conyza spiculosa (Hook. & Arn.) Zardini)

Erigeron stenophyllus Hook. & Arn. (= Conyza gayana Phil.)

Erigeron sumatrensis Retz. (if distinct from E. floribundus; = Conyza sumatrensis (Retz.) E. Walker)

Erigeron trihecatactis Blake (= Conyza trihecatactis (Blake) Cuatrec.)

Erigeron tunariensis Kuntze (= Conyza tunariensis (Kuntze) Zardini)

Erigeron uliginosa Benth. (= Conyza uliginosa (Benth.) Cuatrec.)

Erigeron variifolius Blake (= Conyza coronopifolia Kunth)

Erigeron pazensis usually is not included among these species, but the habit and general aspect suggest that it belongs here. Solbrig (1962, p. 37) noted that it is “A species morphologically similar to Conyza, it is undoubtedly an Erigeron due to the preponderance of tubular over ligulate flowers, and the ligules, which are clearly longer than the tubes.”

An accurate estimate of the number of South American species generally treated as Conyza has not been developed, but there probably are between 60 and 100 (e.g., see Zardini, 1976). Relatively few of the species are included here.

Cronquist (1943), Cuatrecasas (1969), Zardini (1976), Nesom (1990a), and Thébaud and Abbott (1995) have provided suggestions toward a distinction between Conyza and Erigeron. Group B of Conyza is heterogeneous and likely will prove to be non-monophyletic.

Darwiniothamnus Harling, Acta Horti Berg. 20: 108. 1962. Type: Darwiniothamnus tenuifolius (Hook. f.) Harling

Perennial shrubs, fibrous-rooted; caudex simple or branched; glabrous to strigose; leaves linear to oblanceolate, entire to mucronate, in condensed terminal whorls; stems branching; heads in a condensed-corymbiform capitulescence mostly within the leaves; rays white, strongly coiling; achenes dimorphic, ray 2(-4)-nerved, disc 3–5(-6)-nerved.

D. tenuifolius (Hook. f.) Harling (= Erigeron tenuifolius Hook. f.)

D. lancifolius (Hook. f.) Harling (= Erigeron lancifolius Hook. f.)

Darwiniothamnus, an endemic of the Galápagos Islands, has been treated at generic rank by various authors (e.g., Harling, 1962; Cronquist, 1971; Lawesson and Adsersen, 1987). Infraspecific taxa have been described in each of the two species.

Darwiniothamnus alternifolius, the most recently described species (Lawesson and Adsersen, 1987), does not have significant features of the two species upon which the generic concept was based: the plants lack the shrubby “rosette” habit, the leaves are not in condensed terminal whorls, the heads are not in a condensedcorymbiform capitulescence mostly within the leaves, and the achenes are not dimorphic. Further, the ray floret lamina do not coil and molecular evidence indicates that its closest relationships are elsewhere (Andrus et al., in press); it belongs among the species of Erigeron sect. Meridionales, where it is listed here.

Nesom (1989c) suggested that Darwiniothamnus is related to the primarily Mexican group Erigeron sect. Cincinnactis. Recent molecular evidence (Noyes, 2000a; Andrus et al., in press.) shows that the two Darwiniothamnus species are most closely related to sect. Cincinnactis and the Caribbean sect. Microcephalum.

Hysterionica Willd., Ges. Naturfr. Freunde Berlin Mag. 1: 140. 1807. TYPE: Hysterionica jasionioides Willd.

Annual or perennial herbs to subshrubs, taprooted; caudex simple; glandular and otherwise glabrous to hirsute or hispid; stems sometimes branched at the base; leaves mostly oblanceolate, entire to pinnatisect, not clasping; heads 1-several, erect in bud; rays yellow or white, not coiling or reflexing; achenes 1–2 mm long, 2-nerved; pappus of scabrid bristles.

H. aberrans (Cabrera) Cabrera

H. bakeri Hicken

H. cabrerae Espinar

H. glaucifolia (O. Kuntze) Solbrig

H. jasionioides Willd.

H. montevidensis Baker

H. nebularis Deble, Oliveira & Marchiori

H. pinnatiloba Matzenb. & Sobral

H. pinnatisecta Matzenb. & Sobral

H. pulchella Cabrera

Overviews of Hysterionica have been provided by Cabrera (1946), Ariza Espinar (1980), and Nesom (1993c, 1994b). Three species from Brazil have recently been added (Matzenbacher and Sobral, 1996; Deble et al., 2004).

Leptostelma D. Don in Sweet, Brit. Fl. Gard. ser. 2. 38. 1830. Type: Erigeron maximus

Erigeron sect. Leptostelma (D. Don) Benth. & Hook., Gen. Pl. 2: 280. 1873.

Perennial herbs, rhizomatous and fibrousrooted; caudex simple; glabrous to puberulent or hispid; stems branched; leaves ovate to oblanceolate, net-veined, entire or toothed, clasping; heads erect in bud; rays yellow to white, not coiling or reflexing; achenes 2(-3)-nerved, glabrous; pappus of 30–40 bristles.

Erigeron camposportoi Cabrera

Erigeron catharinensis Cabrera

Leptostelma maximum D. Don (= Erigeron maximus (D. Don) DC.)

Erigeron meyeri Cabrera

Erigeron tucumanensis Cabrera

Leptostelma tweediei (Hook. & Arn.) Hind & G.L. Nesom (= Erigeron tweediei Hook. & Arn.; Erigeron seneciiformis Blake)

The remaining combinations to Leptostelma are being made by Aristoˆnio Teles in connection with his synopsis of the tribe Astereae in Brazil.

Neja D. Don in Sweet, Hort. Brit. (ed. 2) 299. 1830. Type: Neja gracilis D. Don = Neja filiformis (Spreng.) Ness

Neja sect. Podoneja DC., Prodr. 5: 325. 1836. Type: Neja gracilis = Neja filiformis (Spreng.) Ness

Neja sect. Monogyria DC., Prodr. 5: 325. 1836. Lectotype (Nesom, 1993b): Neja linearifolia DC. = Neja pinifolia (Poir.) G.L. Nesom

Perennial herbs; taprooted; caudex branched; glabrous to glabrate to sparsely pilose; stems usually branched; leaves mostly basal, filiformto lnear-oblanceolate, entire, not clasping; heads solitary, long-pedunculate or on sparsely bracteolate stems, erect in bud; rays yellow or white, not coiling; achenes fusiformcylindric, with 7–10 raised, thick, orangeresinous nerves; pappus of scabrid bristles.

N. dianthifolia (Griseb.) Nesom

N. filiformis (Spreng.) Nees

N. marginata (Griseb.) Nesom

N. nidorelloides DC.

N. pinifolia (Poir.) Nesom

N. pulvinata (Cabrera) Nesom

Nesom (1994b, 1994c) suggested that Neja might be most closely related to Apopyros but molecular data (Noyes, 2000a) indicate that it is probably the sister group to Hysterionica, the genus from which it has been segregated. The six species of Neja occur in southeastern Brazil and adjacent Uruguay, Paraguay, and Argentina, except for the Cuban endemic N. marginata (Nesom, 1993c, 1994b, 2000).