11. Rhexia mariana Linnaeus, Sp. Pl. 1: 346. 1753.
Maryland meadow beauty
Caudices not developed; roots often long and rhizomelike, non-tuberiferous. Stems usually few- to several-branched distally, sometimes unbranched, 20–80 cm, faces strongly unequal, 1 pair of opposite faces rounded to convex, the other narrower, flat or concave, without wings or very narrowly winged, internodes and nodes usually hirsute-villous, rarely glabrous or glabrate, hairs gland-tipped. Leaves sessile, subsessile, or petioles 0.5–1.5 mm; blade linear, lanceolate, elliptic, or narrowly ovate, rarely linear-filiform, 2–4 cm × (5–)8–15(–20) mm, margins serrate, surfaces loosely strigose to strigose-hirsute or villous. Inflorescences diffuse, not obscured by bracts. Flowers: hypanthium ovoid to subglobose, about as long as the constricted neck, 6–10 mm, hirsute-villous, glabrous, or glabrate, hairs gland-tipped; calyx lobes narrowly triangular, apices acute to acuminate, narrowed to linear-oblong extensions; petals spreading, white or pale to dull lavender, 1.2–1.5 cm; anthers curved, 5–8 mm. Seeds 0.7 mm, surfaces longitudinally ridged with contiguous tubercles, papillae, or laterally flattened domes. 2n = 22.
Varieties 2 (2 in the flora): sc, e United States.
As noted by R. Kral and P. E. Bostick (1969), Rhexia mariana is the most abundant and wide-ranging species of the genus. It is sympatric with every other species and hybridizes with, and often takes on characteristics of, other species.
Variety exalbida was formally recognized by C. W. James (1956) as distinct in its white petals and linear leaves and distribution mostly from southern Mississippi to Florida and along the coastal plain to the Carolinas; James noted that differences are quantitative and intergrading. R. Kral and P. E. Bostick (1969) observed that its distinct distribution might support its taxonomic recognition but that intergradation with var. mariana, especially in the Florida panhandle across the outer coastal plain to Texas, suggested that only a single entity should be recognized. The geography of chromosome counts reported by Kral and Bostick indicates that vars. Exalbida and mariana are diploid. With the caveat that the decision is subjective, var. exalbida is treated here as distinct, emphasizing its geographic concentration in the southeastern corner of the species range.
In the concept of R. Kral and P. E. Bostick (1969), Rhexia mariana also includes vars. Interior and ventricosa. The geographic ranges of each of these varieties lie almost completely within that of var. mariana; each of the varieties is tetraploid; var. mariana is diploid. The morphological differences that separate these entities are subtle but they appear to be consistent, and the ploidal differences probably act as isolating mechanisms. Of the alternatives, to treat all as a single species without subdivisions disregards the biology; to treat them as three varieties disregards the apparent isolation, which usually is a significant feature of a species concept.