This ranges across most of eastern and central North America. It is widely scattered across most of Ky., and was formerly dominant in some native grasslands. However, in the Bluegrass region it is known only from a few low rocky ledges along the Kentucky Rv. and a few peripheral sites in transitions to the Knobs. It is also rare to absent in most Appalachian regions, except locally in the southern Cumberland Plateau and in some western transitions. A. gerardii varies greatly across its range, and further study is need; 2n = 20 to 90 (FNA 25). Although there has been much recent genomic analysis and experimental trials of ecotypes, showing significant variation across the species' range (e.g. Johnson et al. 2015. Galliart et al. 2020), there has been little corresponding morphological or cytological analysis. In Ky. the species occurs in diverse and often disjunct habitats: rocky glades, deeper soils, and riverbanks on diverse substrates. Plants along banks of the Big South Fork (in Ky. and Tenn.) and along the Obed Rv. (in Tenn.) have relatively short inflorescence branches, mostly 3.5-6 cm long (versus 7-12 cm); they have mostly just two branches in inflorescences (versus 2-3); and their leaves lack hairs, even at lower sheath summits (D. Estes, pers. comm.). However, no definitive analysis of these trends has been undertaken. In addition to its overall robustness (FNA 25), gerardii can usually be distinguished from other Andropogon species in Ky. by its relatively long ligules (ca. 0.4-2.5 mm versus 0.2-1 mm in virginicus), and by its blades being usually pilose at least near the collar (versus glabrous or hairy but without concentration at collar). When growing as isolated plants among shorter grasses, gerardii can sometimes form conspicuously large dense circular patches up to 5 m across (J. Redden, pers. comm.). Establishment from seed may be generally rare within grasslands. Unfortunately, a smut fungus has recently infested some fields used for seed production (Snetselaar & Tiffany 1991; R. Seymour, pers. comm.).