Lectotypification of Mimosa adpressa

Mimosa adpressa Hook. & Arn. in Bot. Misc. 3: 202. 1833. – Lectotype (designated here): Argentina, Entre Rios, 1837, Tweedie s.n. ( K K000532824! [two stems on lower half and upper right side of sheet]; isolectotypes:  E E00514885! [two stems on right side of sheet],  K K000543690! [two stems at bottom and lower left side of sheet],  TCD TCD0004716! [stem on left side of sheet]).

Typification — According to Art. 9.6 of the International Code of Nomenclature for algae, fungi, and plants (Turland & al. 2018), a syntype is any specimen cited in the protologue when there is no holotype, or any one of two or more specimens simultaneously designated in the protologue as types; and reference to an entire gathering is considered as citation of the included specimens. In the protologue of Mimosa adpressa, Hooker & Arnott (1833: 202) cited two gatherings from Argentina (“Entre Rios, Tweedie”) and Uruguay (“Uraguay, Baird”). Specimens belonging to these gatherings are therefore syntypes. Barneby (1991) mentioned the existence of syntypes both in K and E. We found three specimens of the Tweedie gathering in K (barcodes K000532824, K000556935 and K000556936) and one specimen of the Baird gathering sharing its barcode (K000543690) with a fourth specimen of the Tweedie gathering. We found two further specimens of the Tweedie gathering in E (barcode E00514885) and TCD (barcode TCD0004716).

Among these syntypes, we consider the most appropriate choice of lectotype to be the Tweedie specimen in K with barcode K000532824. This specimen clearly shows the main morphological feature identifying it as Mimosa adpressa, i.e. sessile or subsessile inflorescences. Furthermore, the label is clear and the sheet bears only material of M. adpressa. The lectotype excludes the stem on the upper left side of the sheet, which is annotated as a specimen from a different gathering (Maldonado, Capt. King s.n., barcode  K000532823). At least one of the other syntypes of M. adpressa could lead to misinterpretation if selected as the lectotype. For example, the sheet in K bearing the Baird specimen (barcode K000543690) also bears a duplicate of the Tweedie specimen, as well as a fragment annotated in pencil as M. bonplandii Benth., but without further annotation or labels, all mounted on the same sheet and sharing the same barcode. We also have some doubts about the syntype status of two of the sheets in K: that with the barcode  K000556935 appears to bear the date “1837” on its label, i.e. later than the protologue, and the sheet with barcode  K000556936 could bear material from two different gatherings, according to the handwritten field notes on two of the labels.

Phenology — Flowering from autumn to spring; fruiting from autumn to the beginning of summer (Izaguirre & Beyhaut 2003).

Distribution and ecology — Argentina (Provinces of Corrientes and Entre Rios); Brazil (only in the State of Rio Grande do Sul) and Uruguay (Departments of Artigas, Canelones, Flores, Florida, Maldonado, Montevideo, Paysandú, Río Negro, Salto, Soriano and Tacuarembó), according to Izaguirre & Beyhaut (2003). The species usually occurs in soils with rock outcrops and not well drained.

Fig. 1.

Morphology and habitat details of Mimosa subinermis. – A: habit and habitat; B: indumentum of old branch; C: aculei; D: leaflets closed at midday; E: trunk; F: habitat. – Brazil, Rio Grande do Sul, Caçapava do Sul, Cerro das Mulas, 11 December 2015; photographs: A–E by D. B. Lucas; F by F. Schmidt Silveira.

Conservation status — This taxon has not yet been assessed according to IUCN Red List categories and criteria (IUCN 2012, 2016).

Remarks — Mimosa obstrigosa and M. ramulosa Benth. are morphologically similar to M. adpressa, but M. adpressa can be distinguished by its sessile or subsessile inflorescence, whereas the other two species have long peduncles (5–20 mm long). We share the opinion of Barneby (1991: 619) in considering M. adpressa and M. obstrigosa as distinct species.

Additional specimen examined — Uruguay: Baird s.n. ( K K000543690! [five stems on upper part of sheet; remaining syntype of Mimosa adpressa]).

Taxonomic treatment of Mimosa subinermis

Mimosa subinermis Benth. in J. Bot. (Hooker) 4:385. 1841. – Lectotype (designated by Barneby 1991: 615, as “presumed holotypus”): Brazil, Sellow s.n. ( K K000532610!; isolectotypes:  P P00755953!,  TUB TUB-009629!). – Fig. 1 & 2.

Description — Treelets 2–3 m tall, almost completely unarmed except for some random conic aculei 1.5–3.5 mm long, mainly at bases of old branches and trunk. Branches sparsely covered by retrorse, adpressed, strigose trichomes and a secondary puberulent indumentum, principally on young branches. Leaves bipinnate, 1-jugate; petiole diminutive, 1.4–3.6 mm long, strigose and puberulent; pinnae 12–49 mm long, with 12–38 pairs of leaflets per pinna, sensitive to touch; leaflets concolorous, narrowly oblong, 3–6 × 0.6–1 mm, with 2 main veins on dorsal surface, no veins on ventral surface, both surfaces glabrous, base asymmetric, margin corneous pallid with translucent setae, apex acute. Stipules lanceolate, 2–3.8 × 0.4–0.7 mm, hispid or not, depending on age, with 1 or 2 main veins. Inflorescences capituliform, globose; peduncle 17–26 mm long, densely covered by retrorse, adpressed, strigose trichomes; floral bracts c. 2.7 × 0.3–0.5 mm. Calyx paleaceous, fimbriate, 1.2–1.7 mm long, covering ⅓–½ of corolla length, glabrous. Corolla tubular, 3–3.7 × 0.5–0.8 mm; lobes densely puberulent at apex. Ovary stipitate, obovate, 0.6–0.8 mm long; stipe 0.3–0.6 mm long. Stamens free, exserted, pink-lilac, 5–6 mm long. Fruit a craspedium, 3–10 per capitulum, oblong-compressed, 20–31 × 3.9–4.7 mm, (3 or)4–7-articulated, stipe 0.9–1.9 mm long, valves and replum strigose, apex cuspidate. Seeds brown, ovoid, 3.5–4.2 × c. 2.7 mm; pleurogram present.

Phenology — Flowering from February to May; fruiting during November and December.

Distribution and ecology — Brazil, State of Rio Grande do Sul: Serra do Sudeste in Caçapava do Sul and Santana da Boa Vista. The species grows on sandstone outcrops, in rocky grasslands and in association with forest on outcrops.

Conservation status — This species lacks information about distribution, ecology and threats because there are few records and most of them have inaccurate geographic data (absence of geographic coordinates). Almost all the excursions we undertook to delimit its distribution failed to find the species at the localities of early records. We found only one locality, but with no more than five individuals. In that regard, Mimosa subinermis was evaluated as Data Deficient (DD) according to IUCN categories and criteria (IUCN 2012, 2016).

Remarks — The name Mimosa subinermis has been considered a synonym of M. rupestris, but we consider it to be a distinct species, and it is therefore reinstated here after 143 years. Mimosa subinermis and M. rupestris were first described by Bentham (1841: 385), both from Sellow collections and both on the same page of Bentham's treatment. In the protologue of M. rupestris, it was cited from the State of Rio Grande do Sul in southern Brazil (“Brazil, Sello; Mountains of Rio Jaquhy, Tweedie”), whereas M. subinermis was only generally cited as a Brazilian species (“Brazil, Sello”), without any finer detail about locality of occurrence. The major differences between the two species according to Bentham (1841) were: absence/presence of aculei, the relation of peduncle length to pinna length, leaflet morphology, and calyx length.

Years later, however, Bentham (1875) appeared to have been less certain about those differences and considered Mimosa subinermis to be a synonym of M. rupestris. Bentham clearly also had difficulty distinguishing other taxa of M. subser. Obstrigosae. For example, M. ourobrancoensis (Burkart 1947), from Minas Gerais State, Brazil, was not described until a century after Bentham (1841) published M. rupestris and M. subinermis, even though Bentham had access to material of M. ourobrancoensis. Bentham cited these early collections of M. ourobrancoensis as M. rupestris in Flora brasiliensis (Bentham 1876).

Barneby (1991: 616) also agreed with the synonymization by Bentham (1875) of Mimosa subinermis under M. rupestris, remarking that “M. subinermis, which Bentham himself eventually treated as a taxonomically negligible armed variant of M. rupestris, is the only specimen of its sort known to me. Except for its very few aculei, inserted on one infrastipular rib immediately below random nodes, it appears identical with genuine M. rupestris. Nothing exact is known of its origin or dispersal, and its status remains contingent on rediscovery.” However, here we show that Mimosa subinermis is readily distinguished from M. rupestris by its habit, presence of aculei, branches sparsely covered by strigose trichomes, paleaceous calyx covering almost half of the corolla length, and fruits covered by strigose adpressed trichomes (Fig. 2, Table 1).

Fig. 2.

Comparison of morphological details of Mimosa subinermis (A–D), M rupestris (E–H) and M. ourobrancoensis (I–L). – A, E, I: stem indumentum; B, F, J: leaflets, dorsal surface (left), ventral surface (right); C, G, K: flowers; D, H, L: fruits. – Scale bars: C, G, K = 0.5 mm; A, B, E, F, I, J = 1 mm; D, H, L = 5 mm. – All photographs by F. Schmidt Silveira.

Table 1.

Morphological similarities and differences between Mimosa subinermis and M. rupestris.

Additional specimens examined — Brazil: Rio Grande do Sul: Caçapava do Sul, Rodovia Caçapava to Lavras, 30 May 1976 (fl), M. L. Porto & al. 2210 (ICN 31257); Camaquã to Caçapava do Sul, Feb 2002 (fl), M. Sobral s.n. (FURB 1370); Caçapava do Sul, Apr 2002 (fl), M. Sobral 9533 (MBM 271091); ibidem, Cerro das Mulas, Nov 1987 (fr), M. Sobral & al. 5718 (ICN 81497); ibidem, 11 Dec 2015 (fr), F. Schmidt Silveira 1050 (ICN); Santana da Boa Vista, Passo dos Neves, 14 Jan 1986 (fr), J. N. C. Marchiori 220 (HDCF 002172).