This poorly understood southeastern taxon, and perhaps trifrons (see notes under hispidus), are the only taxa in Ky. that have been included within the largely northeastern section Tholiformes (F). But that section may be an unnatural, miscellaneous complex (L. Alice et al., pers. comm.; FNA, in press), partly originating from various hybrids of hispidus or its relatives with allegheniensis, setosus (Cr), flagellaris (F) or others. R. decor Bailey is included here (Davis 1990, M); it was initially known only from w. Ky. (F). R. aboriginum may be considered just a somewhat hairy variant within the flagellaris group (Bailey 1943). It appears close to roribaccus, but differs in its usually single flowers (versus 2-8), calyx lobes with a prominent spathulate 1-3 mm tip, leaf margins with jagged-incised (versus regular serration), and leaf bases less cordate (Widrelechner 1998). R. aboriginum is mostly recorded from the lower Mississippi Valley, especially west of the river. Some octoploid cultivars have been selected among these plants, perhaps allowing further spread.