This is a relatively uniform, mostly diploid (2n = 34) species that is widespread in thin dry woods and edges across eastern North America, except on much of the southeastern Coastal Plain (K, FNA 21; Stephens et al. 2015). In Ky. there appear to be occasional hybrids with hirsutus (perhaps in tetraploid form), especially in western regions, and with microcephalus (X glaucus Small), especially in Appalachian regions. Unusually robust plants (perhaps autotetraploids) occur to the west of Ky. (Y, FNA 21); see also Qiu et al. (2019).