Herbs perennial, diffuse, without stinging hairs. Leaves opposite; stipules persistent, paired, interpetiolar, free, reflexed at flowering; leaf blade 3-veined, margin serrate; cystoliths punctiform. Inflorescences axillary, sessile, glomerules of unisexual flowers (plants monoecious or dioecious); male glomerules distal; female ones proximal, or sometimes mixed in middle. Male flowers: perianth lobes (3 or)4, connate at middle, valvate, gibbous or mucronate below apex; stamens (3 or)4; filaments inflexed in bud; rudimentary ovary clavate. Female flowers: perianth tubular, slightly compressed, mouth contracted, apex often minutely 2-4-toothed, in fruit enlarged; staminodes absent. Ovary included; style short; stigma ovoid, fimbriate, persistent; ovule orthotropous. Achene enclosed by thin marcescent perianth; pericarp crustaceous and lustrous. Seeds with endosperm; cotyledons ovate.