Gymnagathis Stapf (1892), not Schauer (1843); Stapfiophyton H. L. Li.

Herbs, erect or creeping, sometimes stoloniferous. Stems 4-sided, sometimes succulent or base subwoody. Leaves petiolate to almost sessile; leaf blade with secondary veins (1 or)2 or 3(-5) on each side of midvein, tertiary veins parallel, quaternary veins reticulate but usually inconspicuous, margin usually denticulate or serrulate. Inflorescences terminal, umbellate or cymose panicles; peduncle long; bracts subulate, small, caducous. Flowers 4-merous. Pedicel usually 4-sided, 2-bracteolate. Hypanthium campanulate to funnel-shaped, membranous, 4-sided or 8-ribbed. Calyx lobes usually triangular, membranous, apex apiculate. Petals pink, red, purple, or rarely white, oblong to obovate, base oblique. Stamens 8, whorls unequal in shape and length. Longer stamens usually pink to purplish red; anthers oblong to oblong-linear, longer than filaments, opening by 1 apical pore, base lengthened and forked or unappendaged. Shorter stamens pale yellow or white; anthers oblong, 1/3 or 1/2 longer than filaments, base usually not forked. Connective base sometimes minutely inflated. Ovary inferior, campanulate, narrowly ovate, or oblong, apex with a membranous 4-lobed crown, margin ciliate. Capsule campanulate to cup-shaped, apex truncate, 4-lobed, longitudinally dehiscent; hypanthium exceeding capsule, 8-ribbed. Seeds cuneate, small (ca. 1 mm), angular, testa tuberculate.

Nine species: China, Vietnam; nine species (eight endemic) in China.