This variable hexaploid (2n = 102) is widespread across east-central states, but sometimes confused with decepetalus, trachelifolius, hirsutus or other species; occasional hybrids are suspected (FNA 21). H. tuberosus appears to have originated from hybridization of tetraploid hirsutus with diploid grosserratus (Bock et al. 2014). In some eastern states, tuberosus is considered introduced from further west, but in Ky. it appears native on fertile floodplains in general, and even on some calcareous uplands without livstock or dense deer. Without herbivory, this allelopathic species (Filip et al. 2016) can rapidly overcome alien pasture grasses and more browsing-resistant herbs such as Vernonia and Ageratina; see also Shen et al. (2021). In the Bluegrass region it is especially frequent, sometimes growing in woodland edges and old fields on seasonally dry sites. It is uncommon to rare in some western regions of Ky., especially on non-calcareous soils. Pubescence varies greatly in density, with relatively long soft hairs (as in the largely midwestern var. subcanescens Gray and in the "artichoke" cultivars) or with short stiff hairs (as in typical wild plants of Ky.). Stems are virtually glabrous in some wild plants of Ky.