This species is widespread across east-central states, but typical plants occur mostly west of the Appalachians in thin woods on mesic to subxeric calcareous slopes. It flowers distinctly later than ohiensis and virginiana, mostly in Jun-Aug (versus Apr-Jun).In the Bluegrass region, although usually in forested corridors along larger streams and rivers today, a few patches have been found along smaller streams around Lexington (Wolf Run and North Elkhorn). T. subaspera is sometimes confused with virginiana, and may rarely hybridize, but it differs from virginiana, ohiensis and allies as follows (FNA 22, W): leaf blades of the upper stem (and often the lower stem) constricted at their bases to a narrower subpetiolar sheath, the opened sheath narrower than the leaf blade (versus not so constricted, opened sheath about as wide or wider); leaf blades ususually 6-27 x 1-5 cm (versus 4-45 x 0.2-3 cm), with L/W mostly 5-10 (versus 15-20); the lower surface distinctly paler than upper, due to more abundant stomates (versus slightly paler or not at all, with stomates slightly more abundant or about equally dense); stems often flexuous (versus not so).