Mapping is provisional. This is a variable species (2n = 16, 32) of diverse vegetation types in seasonally damp thin woods and openings, mostly reported from southeastern states (F, Cr, FNA 20, Y). Descriptions have varied significantly (see same sources). Superficially, racemosum appears intermediate between lateriflorum (sharing secund-tending heads and relatively short rhizomes) and dumosum (sharing narrow glabrous leaves, much reduced upwards, and short disc corolla lobes) or perhaps lanceolatum; see Semple et al. (2002). Diploids of racemosum and lateriflorum are generally distinct, but tetraploids appear to intergrade more often (J. Semple, pers. comm.). Several atypical colls. from Ky., including some formerly identified as "A. vimineus Lam." (from BATH, CAMP, GARR and ROWA), suggest hybrids with lateriflorum, dumosum or even pilosum. But many other Ky. plants have been referred to var. subdumosum (Wieg.) Nesom, with a description that appears transitional to S. lanceolatum (e.g. F; see also Y and W). Var. subdumosum has not been recognized in some recent treatments. Within southeastern states, racemosum generally appears closest to lanceolatum but reportedly differs as follows (Cr, Y, FNA 20): pappi 2.5-3.5 mm long (versus 5.5-6 mm); heads smaller, with involcucres mostly 2.5-4 mm high (versus 4-7 mm), rays mostly 4-8 mm long (versus 6-12 mm) and disc florets mostly 10-20 (versus 20-40); inflorescence branches often recurved, with slightly secund heads (versus racemose with terminal clusters of heads), bracts 5-15 and sometimes grading into phyllaries (versus 1-5, not grading into phyllaries); leaves generally smaller, the basal mostly 1-4 x 0.5-1 cm (versus 5-15 x 1-2 cm), the distal mostly 1-6 cm long (versus 3-10 cm).