This relatively uniform diploid (2n = 34) is widespread and often weedy across southeastern states in open habitats. In Ky. it may be loosely associated with diverse remnants of thin woodland or grassland in southeastern regions of the state, but it also seems to be spreading along rights-of-way elsewhere. It was not recorded in Ky. before the 1930s (B), and it may be increasing in old fields as the climate warms. With its tall stature (with rhizomes often poorly developed), narrow leaves and numerous small heads, the species has some resemblance in habit to Eupatorium hyssopifolium or Conyza canadensis. H angustifolius is in the "southeastern perennial clade" of sunflowers (including siphioides and atrorubens), which mostly have red discs and in some cases basally-disposed leaves. This clade occurs in relatively warm regions, often with dry summers and frequent fires; its diploid species have higher genome sizes than other perennials (Qiu et al. 2019).