Description from Flora of China
Limnanthemum S. G. Gmelin.
Perennials [or annuals], aquatic, usually carpeting surface of lakes and ponds, with short basal rhizomes producing many, slender, and petiolelike stolons [or lacking rhizomes]. Stems usually long, floating, sometimes producing rootlets from nodes. Leaves alternate, rarely apparently opposite; leaf blade floating, veins palmate. Flowers clustered at nodes, (4 or) 5merous, distylous or occasionally homostylous. Calyx lobed to near base. Corolla rotate, lobed to near base, rarely less deeply lobed and campanulate, throat with 5 bundles of long fimbriae. Stamens inserted on corolla tube. Style linear. Nectaries 5, attached at ovary base. Capsules indehiscent, few seeded. Seeds compressed or globose, smooth or ornamented.
About 40 species: temperate and tropics; six species in China.