Strophostyles helvola (L.) Elliott

Wild Bean

Strophostyles helvola plant

Family - Fabaceae/Faboideae

Habit - Taprooted forb, usually annual, twining in other vegetation.

Stem - Trailing or climbing, to 3 m, branched, sometimes rooting at nodes, moderately to densely pubescent.

Strophostyles_helvola_stem.jpgStem and flower.

Leaves - Alternate, pinnately trifoliate, petiolate, stipulate. Leaflets rounded or angled at the base, angled or tapered to a bluntly or sharply pointed tip, often with a minute extension of the midvein at the very tip, the upper surface glabrous or sparsely appressed-hairy, the undersurface sparsely to moderately appressed-hairy; the terminal leaflet with a stalk 6-15 mm long, the blades up to 6.5 cm long and 5 cm wide, variously ovate-triangular, oblong-triangular or pear-shaped, asymmetrically ovate, or rhombic, unlobed or with 1 or more commonly a pair of blunt basal lobes.

Strophostyles_helvola_leaves1.jpgStrongly lobed leaves.

Strophostyles_helvola_leaves2.jpgNearly unlobed leaves.

Inflorescences - Headlike clusters of 3-5 flowers, the inflorescence stalk 5-20 cm long, the flower stalks 1-2 mm long, the pair of bractlets closely subtending each flower 3.0-4.5 mm long, as long as or longer than the calyx tube.

Strophostyles_helvola_bract.jpgBract.

Flowers - Calyces with the tube bell-shaped, 1.5-3.0 mm long, sparsely hairy, the lobes 1.5-3.0 mm long. Corollas papilionaceous, pinkish purple to pink, fading to greenish yellow, the banner 6.5-12.0 mm long, the wings 7-9 mm long, the keel 8-12 mm long and abruptly constricted above the midpoint into a beaklike tip, this relatively slender and usually sharply curved or twisted to the side.

Strophostyles_helvola_flowers.jpgFlowers.

Strophostyles_helvola_flowers.jpgFlower.

Strophostyles_helvola_ff.jpgFlower and fruit.

Fruits - Legumes, linear, terete, sessile, 3-9 cm long, 4-10 mm wide, sparsely hairy to nearly glabrous at maturity, 4-10 seeded. Seeds 5-8 mm long, the surface sometimes appearing waxy, brown, sometimes faintly mottled, pubescent with white-woolly patches.

Strophostyles_helvola_fruits.jpgFruits.

Flowering - June - October.

Habitat - Forests, streambanks, pond margins, prairies, savannas, glade margins, pastures, open disturbed areas.

Origin - Native to the U.S.

Lookalikes - Strophostyles leiosperma, S. umbellata.

Other info. - This twining plant is found throughout Missouri, and across the eastern half of the continental U.S. It occupies a variety of habitats which are somewhat difficult to characterize, though perhaps most commonly found along rivers.

The plant is easily recognized as a wild bean by its characteristic flowers and fruits, but identification to species sometimes requires close examination. Leaves with pronounced lobing always indicate S. helvola, but the lobing is highly variable and can sometimes be difficult to discern, as the photos above show. A more reliable character is the length of the tiny bractlet located just behind the calyx. In S. helvola this is at least as long as the calyx tube (ignore the calyx lobes - see photo above).

Photographs taken at Shaw Nature Reserve, Franklin County, MO, 8-26-2006, 9-10-2015, and 9-12-2018, in Pacific, St. Louis County, MO, 7-27-2015, and in Route 66 State Park, St. Louis County, MO, 9-3-2019 (SRTurner).



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