Mapping remains somewhat tentative. This largely Appalachian and northeastern species has often been confused with trachelifolius, tuberosus and other species, and there may be some hybridization (J. Campbell, in prep.). H. decapetalus is largely unknown in midwestern regions (in and around Mo.), where trachelifolius can occupy similar habitats. There appears to be little overlap of ranges within Ky. Diploids (2n = 34) are reportedly restricted to Appalachian and Atlantic regions. These tend to be generally less robust, and their leaves are usually smaller, less coarsely serrated, and with shorter guard-cells, but they may not be reliably distinguished (Heiser et al. 1969); see also Qiu et al. (2019). Most plants in Ky. may be autotetraploids (pehaps especially in more mesic woods). But D.M. Smith tentatively identified some colls. as diploids, including those mapped in BELL, MART and MCRE by Smith (1960) and Heiser et al. (1969); the locally abundant plants of mesic to subxeric calcareous ridges in the Knobs (e.g. ESTI) may also be diploids. H. decapetalus is often confused with tuberosus; see FNA 21 for details. It tends to have smaller leaves, with more serration, less pubescence, and less winged petioles. Plants are generally shorter, and do not form distinct tubers. Flowering is generally earlier, with phyllaries more elongated and less glandular. Seeds are generally smaller, but with longer scales. Both decapetalus and tuberosus differ from the strumosus complex (including trachelifolius and eggertii) in their leaves, which have more distinct petioles, wider blades with less elongated shape, less glandularity and lack of relatively long stiff hairs. Their heads tend to be larger, but clearcut differences in heads may not exist. See also notes under Heliopsis helianthoides, which is sometimes confused.