Strophostyles helvola

Annual twiner to 1 m; lfls ovate to rarely oblong, 2-6 cm, sparsely pilose at least beneath, some of them commonly with a lateral lobe on one or both sides, or with concave lateral margins; peduncles 0.5-3 dm; fls few-several, 8-14 mm, pink-purple, turning greenish; cal-tube glabrous or with a few appressed hairs; bracteoles lanceolate, acute, usually glabrous, extending at least to the sinuses of the cal; fr 4-9 cm, sparsely appressed-hairy; seeds 5-10 mm, persistently woolly; 2n=22. Dry sandy soil, often on cinders; Que. to Minn. and S.D., s. to Fla. and Tex. (S. missouriensis)

Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.

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From Flora of Indiana (1940) by Charles C. Deam

Infrequent throughout the state as shown on the map. There are no reports from the north-eastern part of the state, but it is, no doubt, more or less frequent in ballast along railroads where I rarely botanized. This species prefers a sandy or sandy, clay soil and is commonly found in ballast along railroads, along roadsides, on wooded slopes, sand bars and sandy shores of streams, on the dunes, and in fallow fields.

……

Indiana Coefficient of Conservatism: C = 3

Wetland Indicator Status: FAC

Diagnostic Traits: annual vine with trifoliate leaves; leaflets deltate-ovate, often with incipient basal lobe, sparsely hairy beneath; bracteoles as least as long as adjacent  calyx tube; calyx 4-lobed, glabrous or hairs limited to lobes; legumes rounded, 4.5-9 cm.