Herbs robust, 3–8 dm, glabrous or sparsely villous. Stems slen­der, erect, solitary or clustered, many-branched, from woody rootstock or rhizomes; branches spreading at 30–70º, moderately to strongly zigzag. Leaves: stipules persistent, asymmetrically ovate-elliptic, 2.5–3.5 × 1.5–3 cm, base cuneate to cordate, apex acuminate; petiole 2.5–4(–5) cm; leaflet blades elliptic to obovate or rhombic, 3–6(–8) × 2–3.2 cm, lateral veins 6–9 pairs, conspicuously net-veined abax­ially, apex acute, obtuse, or emarginate, surfaces gla­brous. Peduncles 4–9(–11) cm; bracts semipersistent, ovate, 6–8 × 3–5 mm. Racemes 7–30-flowered, 12–20(–30) cm; flowers scattered. Pedicels 6–16 mm, glabrous or sparsely villous. Flowers 2–2.3 cm; calyx 8–10 × 7–8 mm at limb, lobes 2–3 mm, much shorter than tube; wing petals elliptic, keel petals asymmetrically oblong-elliptic; ovary sparsely villous; ovules 9–14. Legumes irregularly divergent, straight, 3–6 × 0.4–0.6 cm, inconspicuously pubescent. Seeds 2–8, tan, oblong, 3–4 × 2 mm, short-beaked. 2n = 36.

Phenology: Flowering (Apr–)May–Jun.
Habitat: Mesophytic lower mon­tane evergreen forests.
Elevation: 100–1200 m.

Distribution

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Calif., Oreg.

Discussion

Thermopsis gracilis is readily distinguished from the closely allopatric T. californica and T. montana by its divergent fruits, spreading branches, and glabrous to sparsely pubescent foliage. The species is most closely related to T. robusta, which also has divergent fruits but which differs in its very robust habit, densely pilose vestiture, and longer calyx lobes.

Selected References

None.

Lower Taxa

None.