Herbs, annual, monoecious. Stems prostrate or ascending, diffusely branched, terete, not jointed or armed, not fleshy. Leaves alternate, petiolate; blade rhombic-ovate to suborbicular, base abruptly short-cuneate, margins repand-dentate, apex rounded or acute, sparsely covered with inflated unicellular trichomes (scurfy when dry). Inflorescences staminate and pistillate flowers in mixed clusters in axils of nearly all leaves. Staminate flowers: perianth segments usually 4; stamens usually 4; rudimentary ovary present. Pistillate flowers: perianth segments becoming marginally connate, 4-lobed; stigmas 2, filiform. Fruits utricles, enclosed by enlarged, compressed perianth; pericarp appressed to seed, thinly membranous. Seeds vertical, ovate to triangular-ovate; seed coat reddish brown, thick, membranous; embryo subannular, surrounding perisperm.