Description from Flora of China
Herbs annual or subshrubs, glabrous or shortly hairy. Stem much branched; branches jointed, terete or ribbed. Leaves opposite, sessile, triangular-ovate, leathery, margin entire or denticulate, apex acute. Flowers small, bisexual, with 2 bractlets. Perianth segments 5, oblong or oblong-lanceolate, papery, 1-veined, abaxially with a recurved, winglike appendage. Disk 5-lobed; lobes obtuse at apex. Stamens 5, inserted on disk; filaments subulate; anthers ovate-cordate, apex obtuse or finely mucronate. Ovary ovoid or subglobose, compressed; ovule subsessile; style short; stigma capitate, 2-divided. Utricle enclosed in perianth; pericarp membranous. Seed vertical, ovoid or globose, compressed; testa membranous; embryo spiral or planospiral; perisperm absent.
About six species: mainly in C Asia; one species in China.