Distinction of heterophylla from americana is treated traditionally here at the species level but this may not be tenable (FNA 6). Much variation within North American Tilia appears to be continuous (Hickok & Anway 1972, Hardin 1990, McCarthy & Mason-Gamer 2016, 2020); however six species were recognized by Sargent (1926) and 14 by Sm. In recent treatments (Pigott 2012, W), it has seemed reasonable to treat these taxa as varieties or subspecies of one North American Tilia species, together with the southeastern T. carolinianum P. Mill. and the Mexican T. mexicana Schltr. (which may be most distinct). The largely Appalachian heterophylla is distinguished by "a predominance of stellate or fasciculate trichomes [hairs]" on lower leaf surfaces, peduncles and pedicels; simple "acicular" hairs are also present (Hardin 1990). The largely northeastern americana typically has only acicular hairs, but in apparent introgressants, the more complex hairs are mixed to various degrees. Ky. and Tenn. (Ch) are in the zone of overlap between these two taxa, and there is probably much genetic exchange. They have similar distributions in Ky. and Tenn., both being rare to absent in much of the Mississippian Plateaus and Coastal Plain. In the original forests of Ky., Tilia in general was most common in Appalachian regions; it was much less common elsewhere, except locally in ravines along the Ohio Rv. and its major tributaries (Barton 1919, Campbell 1989). Included here are records of Jones (1968), Little (1971 as triangles), and Gm (as open dots). Several colls. mapped here (including BALL at KY) are less densely stellate-pubescent than typical plants, suggesting transitions to americana, or perhaps just shade leaves.