This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol2", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Psoralea linearifolia T. & G. Fl. N. A. I: 300. 1838.
Erect, 1°-2° high, widely branching; stems not always glandular, glabrous, or sparingly pubescent with appressed hairs. Stipules 1 1/2"-3 1/2" long, lanceolate or setaceous; leaves sessile or short-petioled, 1-3-foliolate; leaflets 5"-15" long, 1 -2" wide, linear, rugose, glandular, glabrous or with a few appressed hairs; peduncles 1'-9' long; flowers blue, loosely scattered, 1-4 together on slender pedicels 2"-4" long; bracts 1" long, ovate, acuminate; mature calyx campanulate, 2" long, glandular, slightly pubescent; pod 4" long, narrowly ovoid or oblong, glandular, with a short stout straightish beak; seed flat, oblique, dark brown..
Psoralea collina Rydberg, Fl. Neb. 21: 54. f. 6, 7. 1895.
Ascending or diffuse, somewhat grayish-pubescent, 1°-2° high. Stipules narrow, 1"-4" long; leaves 3-foliolate, or sometimes 5-foliolate; leaflets obovate or oblanceolate, mucronate, mostly glabrous above; bracts pointed, l 1/2"-2" long; peduncles slender, 1'-4'long; flowers about 3" long; calyx-segments linear-lanceolate, much shorter than the ovate pod, the lower one a little longer than the others; pod 2i"-3" long, tipped with a flat straight beak about l 1/2" long.
Hillsides, western Nebraska. July-Aug.
Psoralea digitata Nutt.; T. & G. Fl. N. A. 1: 300, 1838.
Canescent with appressed hairs, slender, erect, widely branching, 1°-2° high. Petioles shorter than or sometimes a very little exceeding the leaves; stipules linear, 1 1/2"-2" long; peduncles much elongated, often 3-5 times as long as the leaves; leaflets 5, or of the upper leaves 3, digitate, short-stalked, oblong-linear or oblanceolate, 9"-18" long, 2"-3" wide, mostly obtuse or mucronulate at the apex, narrowed or cuneate at the base; inflorescence spicate, interrupted, the blue flowers short-pedicelled or sessile in clusters of 3-5; corolla 4"-5" long, exceeding the broad mucronate bracts; calyx-lobes acute; pod ovoid, flattish, pubescent.
Prairies and hills, South Dakota to Colorado, Kansas and Texas. June-July.
Psoralea incana Nutt. Fraser Cat. Name only. 1813.
Erect, widely branched, densely silvery pubescent with white appressed hairs throughout. Stem often zigzag, 1°-3° high; petioles shorter than or equalling the leaves; stipules narrowly linear, 3"-4" long; leaflets 3-5, digitate, very short-stalked, oval, oblong or obovate, obtuse and mucronate or acutish at the apex, narrowed or rounded at the base, 8"-15" long, 3"-6" wide; peduncles exceeding the leaves; inflorescence spicate, interrupted, the blue flowers sessile, about 4" long, in clusters of 2-4; bracts lanceolate, slightly longer than the corolla, persistent; calyx-lobes lanceolate; pod ovate, straight-beaked.
Prairies and plains, Wisconsin and Minnesota to North Dakota, Saskatchewan, Alberta, Missouri, Colorado and New Mexico. June-Aug.