This is a widespread southeastern species, even in its narrow sense as a diploid (2n = 22), excluding the tetraploids interior and ventricosa (Nesom 2012; FNA 10). Itt is generally restricted to strongly acid soils with more seasonal drying than virginica. See notes under interior, which has also been combined as a variety in the past. Nesom (2012) reviewed the status of mariana, sensu stricto, as follows: "the most abundant and wide-ranging of the species. It is sympatric with all other species and apparently hybridizes with several, the hybrids often seemingly taking on characteristics of the other species. Hybrids and hybrid swarms... with virginica [and others]... have been observed." Within this section of the genus "identifications sometimes are arbitrary" (FNA 10). R. mariana can usually be distinguished from interior and virginica as follows (see also R.J. LeBlond in W): the four stem faces at mid-stem markedly unequal (versus about equal), one pair of opposite faces broader, convex, darker green, the narrower pair concave or flat, pale, the arrangement of broader and narrower faces alternating at each subsequent internode (versus faces almost flat, the angles sharp or winged); roots non-tuberiferous (versus tuberiferous or non-tuberiferous).