Pediomelum argophyllum (Pursh) J.W. Grimes (silvery psoralea, silverleaf scurf-pea)

Psoralea argophylla Pursh

Psoralidium argophyllum (Pursh) Rydb.

Pl. 404 d–f; Map 1789

Rootstock consisting of a stout taproot below a thickened, often short-branched caudex, not tuberous-thickened. Stems 1–3(4), but sometimes appearing loosely colonial from root sprouts, 40–90 cm long, erect, well-branched above the midpoint, densely pubescent with appressed, white to silvery, silky hairs, also gland-dotted (but the glands somewhat obscured by the hairs), the lower few to several nodes often leafless (with the stipules fused). Leaves alternate, palmately 3–5(7)-foliate (3-foliate leaves mostly produced on branches), the petiole 0.5–5.0 cm long. Stipules of well-developed leaves 6–10 mm long, linear, densely hairy and gland-dotted. Leaflets 1.0–3.0(–4.5) cm long, narrowly elliptic to oblanceolate, obovate, or narrowly oblong-obovate, bluntly to sharply pointed at the tip, occasionally rounded or shallowly notched, the upper surface sparsely to densely appressed-hairy, also gland-dotted (but the glands often obscured by the hairs), the undersurface moderately to more commonly densely appressed-hairy. Inflorescences spikes with 2–5 usually well-separated clusters, 4–8 cm long and 1.0–1.5 cm wide at flowering, elongating slightly (if at all) with age, the stalk 3–7 cm long, the bracts 3–9 mm long, linear to broadly lanceolate, tapered at the tip, hairy, the flowers sessile or nearly so. Calyces uniformly woolly-hairy, 4–6 mm long at flowering (becoming enlarged to 7–10 mm at fruiting), the tube 2–3 mm long, somewhat pouched at the base, the upper lobes 1.0–1.5 mm long, the lowermost lobe 3–4 mm long. Corollas 7–11 mm long, usually deep blue to purplish blue, the banner sometimes with a white spot toward the base. Filaments with the fused portion 4–5 mm long, the free portion 0.5–1.0 mm long. Fruits with the body 5–8 mm long, 3–4 mm wide, oblong to oblanceolate in outline, woolly-hairy (sometimes less densely so toward the base), not gland-dotted, tapered abruptly to a short, straight, hairy beak 3–5 mm long, the surfaces somewhat leathery, dehiscing irregularly transversely. Seeds 4–5 mm long. 2n=22. May–July.

Uncommon in northwesternmost Missouri and disjunct in Ralls County; introduced in Jackson County (Montana to New Mexico east to Wisconsin, Missouri, and Texas; Canada; introduced in Illinois). Loess hill prairies, bottomland prairies, and tops of bluffs; also railroads.

Pediomelum argophyllum is distinguished by the silvery-hairy, branched stems, palmately 3–5-foliate leaves, small bluish flowers, and densely hairy fruits. The species is variable in the density of the pubescence. McGregor (1986) noted that although the species has sometimes been described in the botanical literature as producing rhizomes, in his excavations new sprouts appeared exclusively from adventitious buds along the lateral roots.