Description from Flora of China
Herbs, annual, decumbent or creeping, adventitiously rooting at nodes, glabrous. Stem ± 4-angled. Leaves opposite or alternate, sessile. Flowers solitary or infrequently paired, sessile or subsessile, 6-merous, actinomorphic. Floral tube broadly campanulate, broader than long, thinly membranous, 8-12-veined; sepals short; epicalyx segments linear, long. Petals 6 or absent, pale, small, caducous. Stamens (2-)6, deeply inserted. Ovary sessile, ± globose, incompletely 2-loculed; style short; stigma capitate. Capsule dry, thin walled, splitting irregularly. Seeds numerous, obovoid, convex-concave, small.
One to three species, arguably distinct from Lythrum: mainly in Europe; one species in China.
(Authors: Qin Haining (覃海宁); Shirley Graham)