Herbs, perennial; base woody, rootstock thick. Stems erect or ascending, usually striate, 30–100(–150) cm, glabrous or sparsely to densely uncinate-puberulent or conspicuously pilose or glabrescent. Leaves trifoliolate; stipules cadu­cous, subulate to narrowly ovate-deltate, 2–6 mm; petiole (10–)20–50 mm; leaflet blades polymorphic, linear, narrowly ovate, narrowly ovate-oblong, ovate, broadly ovate to subrounded, or rhombic, usually thin, rarely thick, papery, apex acute to obtuse, surfaces closely to subdensely appressed pilose, inconspicuously reticulate-veined abaxially, sparsely appressed-puberulent and pilose adaxially; terminal blade 20–100 × 8–65 mm, length 1–8 times width. Inflorescences terminal panicles and axillary racemes, branched, very diffuse; rachis moderately to densely uncinate-puberulent to -pubescent; primary bracts narrowly ovate, 1–3.5 mm. Pedicels (3–)6–12(–20) mm. Flowers: calyx 2–3 mm, pubescent, tube 1–1.5 mm; abaxial lobes 2 mm, lateral lobes 1 mm; corolla lilac to purple, 6–9 mm. Loments: sutures deeply crenate or dentate abaxially, sinuate adaxially; connections adaxial, 1/5–1/3 as broad as segments; segments (2 or)3–5, deltate to rhombic, (4–)5–10 × 3–5 mm, angled abaxially (sometimes obtusely), convex adaxially, uncinate-puberulent to -pubescent; stipe 1–7 mm. 2n = 22.

Distribution

North America, introduced in e Asia (Japan).

Discussion

Varieties 2 (2 in the flora).

Desmodium paniculatum is allied with D. fernaldii, D. glabellum, and D. perplexum, and the four are called the D. paniculatum Group, which is characterized by having straight loments with 3–5 angled segments. These species have been studied intensively by B. G. Schubert (1950, 1950b) and D. Isely (1953, 1983b, 1990, 1998). According to Isely (1990, 1998), D. paniculatum intergrades with both D. perplexum and D. glabellum, resulting in a continuum of variation among the members of the D. paniculatum Group that suggests introgression, including: D. paniculatum × D. perplexum; D. paniculatum × D. glabellum; and D. glabellum × D. perplexum. They are treated here as varieties of a single polymorphic species. The varieties are distinguished by somewhat continuous or overlapping characters.

Selected References

None.

Lower Taxa

Desmodium paniculatum var. fernaldii, Desmodium paniculatum var. paniculatum

Key

1	Leaflet blade surfaces slightly strigose to conspicuously subappressed-villous, sometimes uncinate-pubescent abaxially; stems and petioles glabrescent to conspicuously pilose or uncinate-pubescent.	Desmodium paniculatum var. paniculatum
1	Leaflet blade surfaces uncinate-puberulent on veins, sparsely strigulose abaxially; stems and petioles glabrous or uncinate-pubescent.	Desmodium paniculatum var. fernaldii