These plants have been treated in various ways, often named "racemosa" as a species or as a segregate of the more northern or western relatives, S. simplex Kunth, S. spathulata DC. or S. randii (Port.) Britt. S. arenicola was recently described from Ala. (Keener & Kral 2003). It also occurs in the southern Cumberland Plateau of Tenn. and Ky. along rocky banks of the Cumberland Rv. and its tributaries, plus the Obed Rv. and Emory Rv. (Floden 2012). It is similar to S. plumosa Small, which is known only from the Yadkin Rv. in N.C. (W). Typical arenicola differs from racemosa in its taller involucres (7-12 mm versus 3-7 mm), glabrous achenes (versus strigose), and more open inflorescence. Both species can also be confused with the widespread upland species, erecta, which has 3.5-6.5 mm involucres (Keener & Kral 2003, Floden 2012). Both may be distinguished from erecta (like all Humiles) by the frequent presence of minute glands in inflorescences (at least phyllaries of stressed plants), the general absence of any other pubescence below (versus scabrellous to cilate along leaf margins), and the generally narrower shape of cauline leaves (with L/W mostly 5-10 versus 2.5-5), tapering to more distinct petioles. Also, they tend to have less numerous heads per stem (mostly 10-50+ versus 40-200+), more disc flowers per head (6-16 versus 6-10), and longer disc corollas (4-6 mm versus ca. 3-4 mm). And arenicola, at least, tends to be rhizomatous (versus strictly cespitose in erecta). There is, however, local variation that needs further study; see notes under racemosa (M; Floden 2012, Peirson et al. 2012). Also, an unusual coll. from the Rockcastle Rv. in PULA (KY) suggests a hybrid with speciosa.