This uncommon species is widely scattered on base-rich soils of east-central states: from the Mississippi Rv. to the Ridge-and-Valley, and from La. to Ont. (Turner 1995). It has become rare in Ky. within the past few decades, surviving mostly in rocky calcareous old fields and rough pastures with relatively little fescue or other improvement. Most records date from before 1970 and come from the Bluegrass region. Some historical records suggest association with large trails or licks used by bison or other large herbivores before settlement. Typical hispidissimum (2n = 24) has been treated as a variety of O. molle (2n = unknown) by Cr. or O. bejariense DC. by Turner (1995). A few colls. have appeared somewhat transitional to typical molle; see notes under that name. O. hispidissimum is relatively robust and covered with relatively dense harsh spreading hairs (almost prickly and up to 3-4 mm on stems), with distinct short and long hairs on leaves; corollas are relatively short (6-10 mm); nutlets are 2.5-3 mm long, flared at the base into a collar, and usually lack distinct pits. The genus Onosmodium appears nested phylogenetically in Lithospermum, with L. tuberosum its closest relative; see Weakley et al. (2011) and their cited literature. Combinations are now available for the Ky. species in the latter genus If accepted, O. hispidissimum would then be known as L. parviflorum Weakley, Whitsell & D. Estes. Some older reports of other Onosmodium species in Ky. were probably based on hispidissimum (M): O. virginianum (L.) DC., a more southeastern species (Nelson 1919, Greenwell 1935), and O. carolinianum DC., which may be an early synonym of hispidissimum (Price 1893).