This is a widespread eastern species (K), but somewhat conservative in its concentration in or near remnants of native grassland and open woodland on subxeric to xeric sites with medium acid soils. It tends to increase after fire but may be intensively browsed by deer and rabbits (Krochmal 1975, Colodonato 1993), perhaps related to the N-fixing ability of this species. Segregates need more study. Most colls. from Ky are referable to var. americanus, but some may be at least transitional to other varieties. Some of B's colls. from FLEM (check US) and GRAV (GH) have been identified as var. intermedius (Pursh) K. Koch., which is known primarily from the southeastern Coastal Plain and may be unlikely in Ky. That variety generally has smaller leaves (ca. 2-4 x 1-2 cm versus 4-10 x 2.5-6 cm) and other differences (F, W). Var. intermedius is probably synonymous with C. glomeratus of Rafinesque (1836, 3:55): "in Virginia, Carolina, Alabama, Kentucky &c commonly blended with [americanus]." A coll. of R. Athey (check EKY) from LIVI has been identified as var. pitcheri Torr. & Gray, which is known primarily from the central Mississippi Valley and adjacent hills; its leaves are generally blunt or rounded (versus acute or acuminate) and pilose above (versus glabrous). Var. pitcheri is probably synonymous with C. latifolius of Rafinesque (1836, 3:55): in "Glades of West Kentucky and Tennessee."