As a native plant in Ky., "switch-grass" is now largely restricted to river banks or nearby lowlands. It is especially common along more open sandy or rocky banks of the Ohio Rv., often with much Amorpha fruticosa. The species is tolerant of eutrophic conditions (e.g. Belt 2015). A few records suggest that before settlement it may have occurred more widely in seasonally damp grasslands on uplands of western regions. However, it is becoming widely sown for wildlife habitat or urban uses, and some outlying colls. mapped here may result from these activities. It has become locally frequent on gravelly slopes below guard rails of major highways. Records from probable sowings or escapes are excluded, but such plants are becoming increasing difficult to distinguish from native plants. This species (and others in section Hiantes or Repentia) will probably become transferred to a separate genus (W). Across its broad North American range, virgatum is highly variable in chromosome number (2n = 18 to 108 plus aneuploids), morphology, and habitat (FNA 25, Costich et al. 2010). Some seed planted in Ky. is the relatively robust "Cave-in-Rock" cultivar (2n = 72), which originated from the Ohio Rv. banks in Ill. across from CRIT. Much other seed comes from the Great Plains. Varied selections and cultivars exhibit large differences in overall size, growth rates and competitive performance (Schwartz & Gibson 2014). In general, the species can be distinguished from other common tall warm-season grasses by the tuft of 2-6 mm hairs at base of upper leaf blade surfaces, which includes the ligule.