This native range of this midwestern annual extends locally into Ind., Ky., Tenn. and Miss., but it is rare or adventive further east (K). It is easily confused with umbellata and some records need to be checked. S. leiosperma differs from umbellata as follows (Isely 1990; W): seed glabrous (versus pubescent); legumes permanently pubescent (versus glabrous at maturity); corollas mostly 5-8 mm long (versus 10-15 mm); leaves permanently pubescent above (versus usually glabrate), conspicuously subappressed-villosulous below (versus sparsely hirtellous, strigose or glabrate), mostly 3-10 mm wide (versus 3-20 mm).