Monoecious or dioecious, annual or perennial herbs, without stinging hairs. Leaves 3-costate, opposite, anisophyllous, petiolate, membranous, serrate-dentate; stipules interpetiolar, scarious. Inflorescence a pedunculate axillary, solitary capitulum like discoid cluster of either male or female or more rarely of mixed flowers. Flowers sessile to pedicellate, bracteolate. Calyx 4-5-lobed in male flowers, lobes slightly unequal, imbricate; unequally 3-lobed in female. Stamens 4-5; staminodes scaly in female flowers. Ovary upright, style absent, stigma penicillate; pistillode small in male flowers. Achene flattened, ovate, partly enveloped by persistent calyx.