Strophostyles leiosperma (Torr. & A. Gray) Piper
Slickseed Wild Bean
CC = 2
CW = 5
MOC = 61
Family - Fabaceae/Faboideae
Habit - Taprooted forb, usually perennial, twining in other vegetation.
Stem - To 1 m, twining, sometimes rooting at nodes, densely pubescent with downward angled hairs.
Leaves - Alternate, long-petiolate, pinnately trifoliate. Stipules minute. Leaflets rounded or angled at the base, bluntly pointed at tip, lanceolate to narrowly lanceolate, unlobed, the surfaces moderately to densely appressed-hairy.
Inflorescence - Solitary flowers or compact axillary racemes of 2-5 flowers. Bractlets subtending calyx shorter than calyx tube.
Flowers - Calyces with the tube bell-shaped, 1-2 mm long, densely hairy. Corollas papilionaceous, light pink fading to grayish white, the banner broadly ovate to nearly circular, the wings oblong, shorter than the keel, the keel widest at the midpoint, abruptly constricted above the midpoint into a blunt, upward-arched beaklike tip that is slightly twisted to the side. Stamens 10, 9 of the filaments fused to above the midpoint and 1 filament free.
Fruits - 1.5-3.5 cm long, 2-4 mm wide, moderately to densely hairy at maturity, 3-8 seeded. Seeds 2-4 mm long, the surface smooth, olive brown, often mottled with darker brown or black, glabrous.
Flowering - June - October.
Habitat - Forest openings, prairies, glades, savannas, streambanks, fields. Often on acidic substrate.
Origin - Native to the U.S.
Lookalikes - Strophostyles helvola, S. umbellata. Vegetatively similar to Amphicarpaea bracteata.
Other info. - This species of wild bean occurs throughout much of Missouri, but is rare or absent in the northwestern third of the state. Beyond Missouri it is found in a broad, scattered band in the central third of the continental U.S. This is one of three species of Strophostyles found in Missouri, and the three can be a little tricky to distinguish. S. leiosperma is characterized by narrow, unlobed leaflets, relatively small flowers, and hairy fruits with glabrous seeds. The specific epithet leiosperma, in fact, means "smooth seed." Under favorable conditions the plants can form large mats.
Photographs taken at Shaw Nature Reserve, Franklin County, MO, 8-3-2007; also near Benton, MO, 8-29-2011; and at Don Robinson State Park, Jefferson County, MO, 9-1-2018 (SRTurner).