Isely (1998) provided an adequate treatment of this species, as did Barneby (1998). The latter worker in his map showing the distribution of the two species, C. biflora and C. conferta, reversed the symbols concerned. Mahler (1981) has provided an excellent line drawing of C. biflora.

This taxon was treated as synonymous with Calliandra eriophylla by McVaugh (1987), as discussed under the latter taxon. Isely (1998) accepted its specific status, as did Barneby (1998) and the present author (see discussion under C. eriophylla). Following my original observations (Turner 1959), Isely also noted that, in Texas, C. conferta has a western element with elongate peduncles, the specimens concerned were appropriately mapped. In the present paper, I treat these western elements as constituting a distinct species, C. iselyi, as there are several other characters that also serve to distinguish the taxon, as noted below.

Calliandra eriophylla var. chamaedrys Isely, Madrono 21: 276. 1972. Type: TEXAS. Uvalde Co.: 15 mi north of Uvalde, 26 Jun 1954, B. L. Turner 3642 (Holotype SMU, now housed at BRIT).

This is a widely distributed, highly variable species of Mexico and closely adjacent United States as noted by Barneby (1998). McVaugh (1987), in his Flora Novo-Galiciana, treated C. conferta as synonymous with the present, but I treat the latter as distinct, as does both Barneby (1998) and Isely (1998). The type of C. conferta is from Val Verde County, Texas, and is readily distinguished from the more southern C. eriophylla by its leaves, which possess but a single pair of pinnae, the latter possessing two or more pair on at least some of its branches. I also agree with both Isely and Barneby that C. eriophylla is represented in Texas by at least a few populations, these given the name var. chamaedrys by Isely (1998), as noted in the above synonymy, the type being from Uvalde County, first collected by me in 1954. I have recently recollected the taxon at the type locality and am reasonably certain that Isely's var. chamaedrys is but a fruit-form of C. eriophylla. Indeed, at the type locality of C. eriophylla var. chamaedrys (revisited in the summer of 2000, Turner 20–384 TEX), mature fruits were found to vary from 2.5–9.0 cm long, overlapping completely the reported range of fruits (7–9 cm) reported for var. chamaedrys by Isely in his original description. The isolated collections of his var. chamaedrys from the “New Mexico-Arizona” boundary (as cited by Isely) are presumably but large fruit forms of C. eriophylla collected in the latter area, although Barneby (1998) thought these might be mixed collections made by Wright from western Texas and given incorrect label data. In short, 1 think that the Uvalde collections concerned are but outlier populations of a widespread variable C. eriophylla. Nevertheless, Barneby (1998) retained the variety, but without knowledge of the information presented here. It should be noted that I have collected C. eriophylla at one other site in Uvalde County, this being ca. 3.1 km W of the intersection of highways 55 and 334 in the northwesternmost part of the county, 2 May 1999, Turner 99–260 (TEX).

Calliandra herbacea Engelm. ex A. Gray, Amer. Acad. Arts Sci. Mem., Ser. 2, 4: 1849.

Isely (1998) recognized two varieties under this taxon: a typical var. humilis and var. reticulata (A. Gray) Benson. By Isely's treatment, Texas material belongs to the typical var. humilis. I would treat the var. reticulata, sensu Isely, as a distinct species, the two taxa being essentially sympatric and readily distinct, as noted by Isely (1998). In my treatment of the Legumes of Texas (Turner 1959), I recognized C. herbacea as distinct from C. humilis. Subsequent work has shown that the former is but a form of the latter.

Type: TEXAS: Brewster Co.: ca. 3 km west of Terlingua along highway 170; small limestone hills at base of Reed Plateau next to the Terlingua House of David Lanman, architect and builder (ca. 29°18′N, 103°33′W), 30 Jun 2000, B. L. Turner & Gayle Turner 20–386 (Holotype: TEX. Isotypes: MEXU, NY).

Similis Calliandra confertae Benth. sed pedunculis plerumque 10–25 mm longis (vice 1–5 mm), corollis glabris (vice corolla valde pubescenti), pinnis cum 6–9 jugis (vice 9–13), foliolis brevioribus apicibe plerumque obtusis aut rotundatis (vice plerumque acutus).

Perennial shrublets 15–25 cm high. Stems more or less fractiflex, pubescent with appressed white hairs. Leaves bipinnate with a single pair of pinnae; petioles 0.5–1.0 mm long; pinnae mostly 8–10 mm long; larger pinnae with 6–9 pairs of leaflets, the latter mostly 2.5–3.5 mm long with raised venation, their apices mostly obtuse or somewhat rounded (rarely broadly acute). Flowers 3–6 on axillary peduncles (7)10–26 mm long; calyces sparsely pubescent, ca. ¼-⅓ as long as the petals; corollas glabrous or nearly so, 3–5 mm long, the lobes 1.0–1.5 mm long. Legumes spatulate to linear-oblanceolate, mostly with 3–6 ovules, relatively few of these forming seeds; valves appressed white-pubescent, their apex apiculate.

Representative specimens examined: The University of Texas specimens (LL, TEX) of Calliandra are currently on loan to MEXU, consequently the following cited specimens of C. isleyi are all on file at SRSC. UNITED STATES. TEXAS: Brewster Co.: Packsaddle Mt., ca. 65 mi S of Alpine, 30 Oct 1964, McAfee 224; 65 mi S of Alpine, 29 Jun 1959, McKenzie 329; 1 mi S of Adobe Wall Mt., 12 Jun 1949, Turner 1080; Muskhog Spring, 30 Jul 1938, Warnock C551; Ward Springs, W side of Chisos Mts., 18 Aug 1955, Warnock 13101; Burro Springs, W side of Chisos Mts., 21 May 1955, Warnock & Walme 13201; Amarilla Mt., 7 mi W of Terlingua, 19 Jun 1949, Warnock et al 1168; Buckhill Mt., ca. 45 mi S of Alpine, 27 May 1959, Warnock et al 17829; 20 mi NE of Alpine along highway 67, 8 Jun 1959, Weyerts 117. Presidio Co.: Lefthand Shutup, Solitario, 14 Aug 1984, Clark 365; Tinaja Prieta Canyon, ca 1 mi below the canyon, on a rocky-gravel bluff above the arroyo, 18 Jun 1978, Powell 3274; 25 mi SE Marfa near Alamito Creek, 19 Jun 1949, Warnock et al. 118513; 4 mi S of Shafter, 27 Jul 1947, Warnock 6624; Old Ross Mine area, Chinati Mts., 15 Oct 1962, Warnock 18855.

Calliandra iselyi is largely confined to the Big Bend region of Trans-Pecos Texas (Fig. 2). It has long resided within the descriptive parameters of C. conferta, the latter typified by material collected by Charles Wright in Val Verde Co. (near the present village of Juno), Texas. So far as known the distribution of these two taxa do not overlap, nor do they appear to intergrade.

Both Turner (1959) and Isely (1998) called attention to the distinctiveness of the populations concerned in noting that the peduncular lengths of the two taxa consistently differ. Closer scrutiny of the two taxa in the present study shows that C. iselyi can also be readily identified by yet other characters, including glabrous corollas (rarely a few hairs near the apex of lobes), shorter petioles (0.5–1.0 mm long vs. 1–2 mm long), generally fewer leaflets per pinna (69 pairs vs. 9–13 pairs), the leaflets at midpinna of a different shape, being shorter with mostly obtuse or rounded apices (vs. acute, Fig. 3). In addition to the present illustrations), Powell (1988) provided an excellent sketch of the species, albeit labeled C. conferta. Barneby (1998), in his broad monographic treatment of Calliandra, did not comment upon the morphogeographic patterns which serve to distinguish C. iselyi, but he did review the present manuscript and raised no objections to its description here.

The species is named for my long-time friend, Duane Isely (1918-) , Prof. Emeritus of Botany at Iowa State University, Ames, Iowa, and zealous scholar of the legume family.