J. Jpn. Bot. 88: 166–175 (2013) New Combinations in North American Desmodium (Leguminosae: Tribe Desmodieae) Hiroyoshi OHASHI Herbarium, Botanical Garden, Tohoku University, Sendai, 980-0862 JAPAN E-mail: [email protected] (Accepted on May 11, 2013) Three species groups in Desmodium of North America: D. ciliare group, D. paniculatum group and D. procumbens group are revised for Flora of North America. Each of them is treated as a single species containing one or two varieties. The following four new combinations are published: D. marilandicum var. ciliare (Willd.) H. Ohashi, D. marilandicum var. lancifolium (Fernald & B. G. Schub.) H. Ohashi, D. paniculatum var. fernaldii (B. G. Schub.) H. Ohashi, and D. procumbens var. neomexicanum (A. Gray) H. Ohashi. Desmodium obtusum (Willd.) DC. is regarded to be a synonym of D. marilandicum var. lancifolium; D. glabellum (Michx.) DC. and D. perplexum B.G. Schub. to be synonyms of D. paniculatum; and D. procumbens var. exiguum (A. Gray) B. G. Schub. to be a synonym of D. procumbens var. procumbens. Key words: Desmodium, Fabaceae, Leguminosae, new combinations, North America. Recently, Desmodium of North America can at least identify it with the group.” Under has been the subject of much study, notably by this framework, Isely recognized D. ciliare Schubert (1940, 1950a, 1950b, 1970) and Isely (Willd.) DC., D. paniculatum (L.) DC. and D. (1983, 1990, 1998). “Desmodium traditionally procumbens (Mill.) Hitchc., along with each is considered a ‘difficult’ genus” (Isely 1990, p. of their related taxa, as species groups. The 163). Isely (1990) further stated that Desmodium difficulty in classifying these groups is, however, contains “groups of species whose taxonomy not satisfactorily solved by this approach. Taxa is presently ambiguous or among which the attributed to these groups appear to have been differentiation of kinds is unsatisfactory or recognized by over-weighting such variable overlapping. In such cases, confidently keying characters as type and degree of density of a plant to a name is often difficult. Thus, I indumentum on the stems and leaves and by the have borrowed a device from Flora Europaea size and shapes of the leaves. The problems in (Tutin et al. 1968, p. xv): ‘Where it is difficult the North American species groups are similar to distinguish between a number of closely to those in the Asian species of Desmodium. similar species in a genus, an ad hoc group For example, Desmodium heterocarpon (L.) has been made, and these groups ... are keyed DC. includes many synonyms that were initially out in the main species key.’ ... For example, if distinguished by over-emphasizing superficially the identity of a specimen in the Desmodium discontinuous characters (Ohashi 1973, 1991). paniculatum (L.) DC. group is uncertain, one To correctly distinguish natural taxa, further —166— June 2013 The Journal of Japanese Botany Vol. 88 No. 3 167 analyses of morphological characters and commonly stout .............................. D. ciliare genetic features of the groups are necessary. 4. Stems and leaves with various combinations Until that time when such detailed studies can of characters of D. ciliare and D. be carried out, I have decided to regard each of marilandicum, e.g., stems and leaflets the “groups” as single species, D. paniculatum, glabrate but petioles 1–3 mm long or stems D. marilandicum, and D. procumbens, in my pilose but petioles well developed; pedicels treatment of Desmodium for the Flora of North various in length .............................................. America. Their so-called related species are ......................... D. ciliare × D. marilandicum treated as synonymous or as varieties of the recognized species. Isely (1998) noted, however, that “many populations of Desmodium ciliare are of, or 1. The Desmodium ciliare Group include, plants with various features of D. Plants described in this group as separate marilandicum” (p. 538). “Some plants of D. species are characterized by having similar 2 or marilandicum throughout its range exhibit 3 segmented loments. They include Desmodium various combinations of the characters of D. ciliare (Willd.) DC., D. marilandicum (L.) DC., marilandicum and D. ciliare and are relegated and D. obtusum (Willd.) DC. with D. ciliare × to postulated D. ciliare × D. marilandicum D. marilandicum and D. ciliare × D. obtusum category” (p. 546). This presumed hybrid (Isely 1990, 1998). Isely (1998), Krings (2004), includes “(1) plants with the aspect of D. ciliare, and Raveill (2006), each presented keys to the D. but which are glabrate or have some pubescence; ciliare group, all based on vegetative characters, (2) those with the aspect of D. ciliare, including of which Isely’s is as follows: pubescence, but leaves well petioled; and (3) those with the aspect of D. marilandicum but 1. Leaflets –3 5.3 times as long as wide ............. somewhat pilose” (p. 558). Desmodium ciliare ................................................... D. ciliare × ? × D. obtusum is presumed to be “plants with 1. Leaflets 1.2–3.5 times as long as wide ........2 foliage intermediate between Desmodium ciliare 2. Terminal leaflet generally distinctly longer and D. obtusum and with a mixture of uncinate and narrower than others; medial stems and pilose pubescence (p. 558). sparsely to densely uncinate-pubescent ......... Isely’s (1998) comments indicate that D. ....................................................... D. obtusum ciliare, D. marilandicum and D. obtusum are 2. Terminal leaflet similar to lateral ones; indistinguishable without recognizing the medial stems glabrous to pilose or also with intermediate forms between them as presumed uncinate pubescence. hybrids. No evidence of hybrid origin of these 3. Stems glabrous(-sparsely uncinate- intermediate forms was presented. I recognize puberulent); petioles 1–2.5 cm long; leaflets this group as a single polymorphic species, D. glabrous or with a few hairs; pedicels marilandicum, with three varieties, although the filiform, generally 0.8–1.5 cm long ............... distinction between the vaieties is sometimes ............................................. D. marilandicum ambiguous. A key to the varieties is as follows: 3. Stems generally pilose; petioles and pedicels 1. Terminal leaflet elliptic-ovate to narrowly shorter than above or plants lacking the ovate, 5–7.5 × 2–3.3 cm, apex acute to obtuse above combination of characters ................ 4 ................................................ var. lancifolium 4. Stems conspicuously or thinly pilose(- 1. Terminal leaflet elliptic, ovate, ovate-rhombic uncinate-puberulent); petioles 1–3 mm long, or broadly ovate, 0.9–4 × 0.6–1.7 cm, apex shorter than rachis; leaves subappressed- obtuse ............................................................ 2 pubescent(-glabrate); pedicels 3–8 mm long, 2. Leaves nearly sessile, petioles 1–15 mm 168 植物研究雑誌 第 88 巻 第 3 号 2013 年 6 月 Fig. 1. Holotype of Desmodium ciliare var. lancifolium Fernald & B. G. Schub. (GH). June 2013 The Journal of Japanese Botany Vol. 88 No. 3 169 long; stems and petioles uncinate-puberulent D. marilandicum var. lancifolium (Fernald and mostly pilose; pedicels 3–8 mm long ..... & B. G. Schub.) H. Ohashi, comb. nov. ......................................................... var. ciliare D. ciliare var. lancifolium Fernald & B. G. 2. Leaves petiolate, petioles 12–30 mm long; Schub., Rhodora 40: 437 (1938). [Fig. 1] stems essentially glabrous, petioles sparsely Hedysarum obtusum Willd., Sp. Pl. 3(2): uncinate-puberulent; pedicels (6–)8–19 mm 1190 (1802). long ................................... var. marilandicum H. rigidum Elliott, Sketch Bot. S. Carolina 2: 215 (1823). Desmodium marilandicum (L.) DC., Prodr. D. obtusum (Willd.) DC., Prodr. 2: 329 2: 328 (1825); Schub. in Gray’s Man. ed. 8: 920 (1825); Isely, Native Natur. Leg. US: 547 (1950); Schub. in Man. Vasc. Pl. Texas: 864 (1998); Krings in Vulpia 3: 144, fig. 9 (2004). (1970); Isely, Vasc. Fl. SE US 3(2): 175 (1990); D. rigidum (Elliott) DC., Prodr. 2: 330 Isely, Native Natur. Leg. US: 546 (1998); Krings (1825). in Vulpia 3: 145, fig. 8 (2004); Raveill in Vulpia Meibomia obtusa (Willd.) Vail in Bull. 5: 20 (2006). Torrey Bot. Club. 19: 115 (1892); Schind. in Hedysarum marilandicum L., Sp. Pl. 2: 748 Repert. Spec. Nov. Regni Veg. 23: 357 (1927). (1753). Meibomia rigida (Elliott) Kuntze, Revis. Meibomia marilandica (L.) Kuntze, Revis. Gen. Pl. 1: 198 (1891). Gen. Pl. 1: 198 (1891). Stems and petioles sparsely to densely var. marilandicum uncinate-puberulent. Leaves shortly petiolate; Stems essentially glabrous. Leaves mostly petioles sparsely to densely uncinate-puberulent, petiolate; petioles sparsely uncinate-puberulent, 2–20 mm long; terminal leaflet elliptic-ovate to 12–30 mm long; terminal leaflet ovate, ovate- narrowly ovate, 5–7.5 × 2–3.3 cm, apex acute to rhombic or suborbicular, 1.5–2.5(–4) × 1–1.7 cm, obtuse. Pedicels 4–10 mm long. apex obtuse. Pedicels (6–)8–19 mm long. 2. The Desmodium paniculatum Group D. marilandicum var. ciliare (Willd.) H. Schubert (1950a, 1950b) treated Desmodium Ohashi, comb. nov. paniculatum (L.) DC. and its related species Hedysarum ciliare Willd., Sp. Pl. 3(2): 1196 and clarified the classification of the group by (1802). recognizing D. glabellum (Michx.) DC. and Desmodium ciliare (Willd.) DC., Prodr. 2: describing D. perplexum B. G. Schubert. Isely 329 (1825); Isely, Native Natur. Leg. US: 538 (1983) surveyed the taxonomic relations among (1998); Krings in Vulpia 3: 145, fig. 6 (2004). these