Erect, annual and perennial, monoecious herbs, without stinging hairs; stems prostrate and ascending; cystoliths linear. Leaves distichous, alternate, sessile or very shortly petiolate, asymmetric; stipules fused, intrapetiolar (presence of 2 pairs of stipules indicates that genus has opposite leaves but one leaf of each pair is rudimentary or totally reduced). Inflorescences unisexual, axillary, sessile, consisting of very densely clustered flowers and surrounded by almost free bracts in male inflorescences or by somewhat fused bracts in female inflorescences. Male flowers 4- or 5-merous; tepals generally with a horn-like dorsal appendage; rudimentary ovary absent or indistinct. Female flowers with 3-5 very reduced tepals and 3 scale-like staminodes, sometimes sterile. Ovary ovoid with penicillate stigma. Achene ovoid, small, ejected by reflexed staminodes.
Species +/- 200, often very polymorphic, in the tropics of the Old World; sthn trop. Afr. 3: Angola, Zambia, Zimbabwe, Malawi and Mozambique.