Herbs, perennial, with creeping rhizomes. armed with stinging hairs. Stems often caespitose. Leaves alternate, petiolate; stipules persistent, lateral, free, membranous; leaf blade broad, membranous, irregularly 2-5-veined, secondary veins dichotomously branched, margin coarsely dentate or subincised; cystoliths often botuliform. Inflorescences axillary, pedunculate cymes (male) or sessile glomerules (female), unisexual (plants monoecious); male dichotomous cymes solitary, with filiform peduncles; female clusters sessile in the same or different axils; bracts present. Male flowers: perianth lobes (4 or)5, slightly imbricate, transversely crested below apex; stamens (4 or)5; rudimentary ovary obovoid or urceolate, transparent. Female flowers: perianth lobes 4, unequal, outer (dorsal-ventral) 2 larger, keeled, corniculate below apex, inner 2 smaller, flat, all usually with stinging hairs below apex. Stigma subsessile, penicillate-capitate. ovule orthotropous. Achene straight, ovoid, compressed, invested by the persistent but not enlarged perianth. Seeds erect, with thin endosperm; cotyledons ovate, fleshy.