Thermopsis rhombifolia

Scientific Name: Thermopsis rhombifolia (Nutt. Ex Pursh) Nutt. Ex Richards.
Family Name: Pea (Fabaceae)
Common Name: Prairie thermopsis, goldenpea, yellowpea, buffalo bean, false lupine

Morphological Characteristics:
Habit - native perennial legume with creeping, fibrous rootstocks, that spread to form extensive, loose colonies; mostly unbranched, erect, glabrous stems, 1 to several from a woody crown, 10 to 30 cm (4 to 12 in.) tall.
Leaves - alternate, mostly 3 leaflets, 3 to 6 cm (1.2 to 2.4 cm) long, gray-green, smooth above to silky hairy below, obovoid to elliptical, with prominent heart-shaped stipules at base.
Flowers - typical pea-like flower, arranged in dense, terminal racemes, calyx 2-lipped with bell-shaped tube, corolla bright yellow to golden-yellow, 15 to 20 mm (0.6 to 0.8 in.) long, the uppermost banner petal longest.
Pea Pods – dark gray to dark brown, narrow, flat, somewhat pubescent, generally curved into half a circle or more at maturity, 10- to 13-seeded, constricted between seeds, 6 to 10 cm (2.4 to 4 in) long, opening lengthwise at maturity, dropping seed.
Fruit - seeds 3 to 4 mm (0.11 to 0.16 in) long, dark brown with greenish tint and kidney-shaped.

Blooming: early flowering--beginning late April, with seed maturity June to August; plant generally dies back in August.

Distribution & Habitat: found in nearly all of Montana east of the Continental Divide and in all but northwestern Wyoming; widely adapted to dry uplands on a variety of soils, but occurs on shale outcrops, sandy sites on ridges, hilltops, slopes, and disturbed areas.

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Last Modified: 06/15/2005