Strophostyles helvola (L.) Ell.
Family - Fabaceae
Stems - Thin, herbaceous, twining or trailing, from taproot, often with a reddish-purple tinge, retrorse pilose, single or multiple from base, branching, terete to angled or twisted.
Leaves - Alternate, (lowest few leaves may be opposite), petiolate, stipulate, trifoliolate. Stipules lanceolate, to +5mm long. Petiole to +6cm long, pubescent to strigose. Leaflets ovate to lance-ovate, often lobed, mucronate, entire, glabrous to sparse strigose, to +6cm long, +3cm broad. Lateral leaflets often unequally lobed near base, on petiolules to +/-5mm long. Terminal leaflet often more or less equally lobed at base, on petiolule to +/-1cm long.
Inflorescence - Axillary compact pedunculate raceme. Raceme appearing capitate. Peduncles to 15cm long, retrorse pilose. Flowers 3-7 in raceme. Each flower subtended by small lanceolate-acuminate bract. Bracts to +/-3mm long, equaling or longer than the calyx tube.
Flowers - Corolla papilionaceous, whitish pink or lilac and fading to a yellowish-pink. Standard to 1.4cm long, 1.2cm broad, glabrous. Keel petal lilac-pinkish at base, becoming purplish at apex, curved upward and backward and often resting against the standard. Stamens 10, diadelphous. Style, white, glabrous, curved like keel petal. Ovary terete, green. Calyx bilabiate, glabrous to sparse pubescent, often reddish-green. Upper lip single lobed(with two united teeth), acute, to +2.2mm long. Lower lip 3-lobed. Lateral lobes to 3mm long, acute to acuminate. Central lobe to +5mm long, acute to acuminate. Fruit to +8cm long, subterete, sparse appressed pubescent to glabrous, green (dark brown to black when mature), elastically dehiscent.
Arrow shows bracts subtending the calyx.
Flowering - June - October.
Habitat - Thickets, rich woods, moist ground, roadsides, railroads.
Origin - Native to U.S.
Other info. - This is a frequent plant in Missouri. The flowers are easy to recognize because of the twisted keel petals. The leaves of the plant can be somewhat variable. As you may notice, the leaves in the first picture above are quite different from the leaves in the second picture. Some authors break the species apart into two different varieties based on the leaf shape and fruit size but I won't do that here.
Photographs taken at the Kansas City Zoo, 7-10-00, and at Trinity Episcopal Conference Center, Salter Path, NC., 9-29-02.