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.