Heterotheca subaxillaris (Lam.) Britton & Rusby includes a complex of morphotypes that have been treated in multiple ways nomenclaturally.  The complex of annuals and sometimes perennials in Mexico is very weedy (Semple 2006 FNA).  Robust plants have broadly compound corymbiform arrays of heads on widely diverging branches.  Leaves tend to be less densely spaced on the stems than in H. grandiflora and sessile upper stem leaves tend to be clasping and often more ovate.

Heterotheca subaxillaris range draft Semple

Semple (2006) in Flora North America recognized just two geographically distinct races that differed in the numbers of large hairs on the ends of the phyllaries (Semple 2004) illustrated phyllary variation.