Mapping here is tentative; there is considerable variation among specimens, with some suggesting hybrid origins. This taxon was recognized as a species by F and others, with a wide range from midwestern to southeastern regions, but it has been largely ignored since then. Heiser et al. (1969) indicated that it may be the tetraploid form of strumosus (with 2n = 68), and suggested treatment as a variety or subspecies. H. trachelifolius is generally distinct from typical octoploid strumosus (2n = 102) within the core of its range, but there appears to be some intergradation in regions of overlap. There has also been much confusion, and probably some introgression, with decapetalus and other tetraploids, especially with hirsutus in w. Ky. and w. Tenn. H. trachelifolius differs from typical strumosus in its more well-developed leaves, which are usually subtruncate (versus more gradually tapering), with the non-winged portion of petiole ca. (0.5) 1-2 (3) cm long (versus (0.3) 0.5-1 (1.5) cm); lower surfaces are deep or pale green (versus grayish, whitish or glaucous), pubescent on veins and often throughout (versus often glabrous except on main veins); margins are serrated with teeth ca. 1 mm high (versus weakly serrated to subentire). Stems are often setose to scabrous (versus usually glabrous or glabrate), and usually dry to a blackish hue (versus pale to blackish). H. trachelifolius flowers mostly in mid-July to late Aug (versus Aug-Sep). Plants have been cultivated for over 250 years in British gardens (P. Miller, 1768: Gardner's Dictionary, 8th edition), and have been available from a few nurseries in the U.S.A. (e.g..Tripple Brook Farm in Mass., formerly at tripplebrookfarm.com), and from the author's (JC) garden.