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.