Description from Flora of China
Herbs, diffusely creeping, villous. Stems slender, much branched, rooting from nodes. Leaves dimorphic. Stem leaves opposite, flat, orbicular. Branch leaves crowded, needlelike, involute. Flowers axillary, solitary. Calyx deeply 5-lobed to base, lobes narrow. Corolla white or rose, actinomorphic; lobes 5, subequal, as long as tube. Stamens 4, included, equal, inserted at base of corolla. Style shorter than or as long as stamens; stigma subulate or 2-lobed. Capsule septicidal lengthwise, valves entire or 2-parted. Seeds numerous; seed coat smooth.
One species: tropical and subtropical Asia.