Herbs delicate, 2–8(–10) dm, glabrate, appressed-pubescent, or thinly villous. Stems slender, erect, solitary or clustered, mod­erately or few-branched, from woody rootstock or rhizomes; branches ascending at 20–45º, weakly or moderately zigzag. Leaves: stipules persistent, widely ovate or elliptic, 1.7–4.5 × 0.7–2.5 cm, base oblique to cuneate, apex acuminate or acute; petiole 1–4 cm; leaflet blades elliptic or obovate, 3.5–8 × 0.7–3(–5) cm, lateral veins 6–11 pairs, conspicuously net-veined abaxially or not, apex acute or obtuse, sometimes short-mucronate or emarginate, surfaces sparsely appressed-pubescent or glabrous. Peduncles 2–8 cm; bracts semipersistent, narrowly elliptic or elliptic to widely ovate, 6–10 × 2.5–6 mm. Racemes 6–25-flowered, 4–25 cm; flowers in whorls of 2 or 3 or scattered. Pedicels 3.5–5 mm, villosulous. Flowers 1.6–2.2 cm; calyx 9–11 × 5–8 mm at limb, lobes 3–5 mm, shorter than tube; wings and keel petals asymmetrically oblong-elliptic; ovary velu­tinous or densely appressed-pubescent; ovules 10–16. Legumes ascending, straight, 4.5–6.5 × 0.4–0.6 cm, villosulous or appressed-pubescent. Seeds 6–16, brown-black, oblong, 3.5–5 × 2.5–3 mm, beaked.

Distribution

North America.

Discussion

Varieties 2 (2 in the flora).

The strictly erect fruits distinguish Thermopsis montana from T. gracilis and from the superficially similar T. divaricarpa. Intermediate populations and possible hybrids are discussed under T. divaricarpa by C. J. Chen et al. (1994).

Selected References

None.

Lower Taxa

Thermopsis montana var. montana, Thermopsis montana var. ovata

Key

1	Herbs 2–7 dm, appressed-pubescent to thinly villous; stems solitary or clustered, few-branched, from woody rootstock or rhizomes; leaflet blades not conspicuously net-veined abaxially; floral bracts elliptic to widely ovate.	Thermopsis montana var. montana
1	Herbs 5–8(–10) dm, glabrate to sparsely appressed-pubescent; stems clustered, several-branched, from woody rootstock; leaflet blades conspicuously net-veined abaxially; floral bracts narrowly elliptic.	Thermopsis montana var. ovata