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..
Perennial glandular-punctate herbs, with long or deep roots, odd-pinnate leaves, and pink purple or white spicate or capitate flowers. Calyx-teeth nearly equal, rather broad, shorter than the tube. Petals on long slender claws; standard oblong or cordate; wings and keel-petals similar to each other, their claws adnate to the sheath of the stamen-tube almost to its summit. Stamens 5, alternate with the petals. Ovary sessile, 2-ovuled; style subulate. Pod included in the calyx, 1-2-seeded. [Greek, referring to the united petals and stamens.]
About 50 species, natives of North America and Mexico. Type species: Petalostèmum cándidum Michx. The generic name Kuhnistera Lam., used for these plants in our first edition, is better restricted to its type species, K. pinnata (Walt.) Kuntze, of the Southern States, which has the spikes subtended by an imbricated involucre, and long bristle-like calyx-teeth. * Foliage glabrous or very slightly pubescent.
Flowers white; leaflets 3-9.
Leaflets oblong, linear-oblong or oblanceolate; spikes cylindric or oblong.
Calyx glabrous or nearly so.
Stem little branched; spikes cylindric: leaflets 1/2'-1' long, thin.
Stem much branched; spikes oblong; leaflets smaller, firm.
Leaflets narrowly linear; heads globose or short.
Flowers pink or purple.
Leaflets 3-5; calyx silky-pubescent.
Bracts glabrous; leaflets mucronulate.
Bracts silky-pubescent; leaflets obtuse.
Leaflets 13-31; calyx glabrous.
** Foliage silky-pubescent; leaflets 9-17.
1828. P. compactus Swezey, Nebraska Flow. Pl. 6. 1891. Kuhnistera compacta Kuntze, Rev. Gen. Pl. 192. 1891.
Erect, dotted with sessile glands, branched, 1°-2 1/2° high. Leaflets 5-7, glabrous, short-stalked, oblong-lanceolate or linear-oblong, acute or obtusish, dotted beneath, 6"-12" long, about 2" wide; peduncles terminal, elongated, not bracted; spikes cylindric, 2'-6' long, about 6" thick, the rachis pubescent; flowers white or nearly so, about 2" long; bracts awn-pointed, longer than the densely villous-pubescent calyx; wings and keel-petals oblong; standard cordate; pod pubescent, enclosed by the calyx.
In dry soil, South Dakota to Nebraska, Kansas, Colorado and Wyoming. July-Aug.