Rhexia is a genus of 11–13 species of flowering plants in the family Melastomataceae (order Myrtales), commonly known as meadow beauties. It is the only genus in the family that is predominantly temperate and North American rather than pantropical, and its striking flowers make it one of the most recognizable wildflowers of the southeastern United States.
Plants are herbaceous perennials. The opposite leaves are simple, ovate to lanceolate, and display the acrodromous venation — prominent arching lateral veins running toward the leaf tip — that is characteristic of the Melastomataceae family. Stems are distinctive in having four faces: one pair of faces is broader and convex, the other is narrower and concave. Flowers are radially symmetrical, 2–3 cm across, and typically pink-purple to white, with four petals, four sepals, and eight stamens bearing conspicuously long, bright yellow anthers that curve counterclockwise. The sole exception is Rhexia lutea, which bears yellow flowers. Seeds are coiled (cochleate) in most species, but not in R. alifanus.
Like most Melastomataceae, Rhexia flowers are adapted for buzz pollination: visiting bees grip the anthers and vibrate their flight muscles to release pollen. Rhexia virginica, the best-studied species, is pollinated by bumblebees and changes flower color after pollination — a classic signal to redirect pollinators toward unpollinated blooms.
Taxonomy within the genus has been revised several times. The most recent classification, by Nesom (2012), recognizes 13 species grouped into four sections: Sect. Rhexia (the largest group, including R. virginica, R. mariana, and R. cubensis), Sect. Cymborhexia (containing only R. alifanus), Sect. Brevianthera (R. petiolata and R. nuttallii), and Sect. Luteorhexia (R. lutea).
Distribution
Rhexia is distributed across the temperate southeastern United States and the Caribbean, ranging from Nova Scotia south to Florida and the West Indies (Cuba, Hispaniola, and Puerto Rico), and west to eastern Texas. Unlike most of its family, which is pantropical, Rhexia is concentrated in wet meadows, coastal plain marshes, sandy wetlands, lake edges, pine woods, and road-side swales.
Ecology
Most Rhexia species colonize open, frequently disturbed habitats — particularly areas maintained by recurrent fire or land reclamation — as well as naturally wet, nutrient-poor soils. Flowers are adapted for buzz pollination by bees, especially bumblebees, which vibrate their flight muscles to dislodge pollen from the poricidal anthers.
Taxonomy Notes
Two foundational treatments by James (1956) and Kral & Bostick (1969) divided the genus into Series A (short, straight anthers: R. petiolata, R. nuttallii, R. lutea) and Series B (long, curved, descending anthers: eight species). Nesom (2012) reorganized the genus into four sections — RHEXIA, CYMBORHEXIA, BREVIANTHERA, and LUTEORHEXIA — recognizing 13 species by elevating two tetraploid R. mariana varieties to species rank on the basis of allopatric distribution and stem morphology.
