Fls us. perfect, in clusters on simple or branched racemes or spikes. Outer 3 tepals small, thin; inner 3 enlarging and hardening in fr., with or without tubercles on midribs. Stamens 6, basifixed. Fr. triquetrous or trigonous, invested by persistent hardened per. Annual to perennial herbs, us. with deeply descending stout taproot; lvs alt., stipules ochreate. Subcosmopolitan genus with some 150 spp., the N.Z. pair endemic.

Glabrous, monoecious annuals with lax or prostrate stems. Lvs cauline, ± oblong with broad bases; ochreae soon lacerate. ♂ fls in terminal or axillary, pedunculate clusters; pedicels filiform; perianth segments (5)-6, free, green; stamens 4-6. ♀ fls in sessile axillary fascicles; perianth segments (5)-6, connate below to form a triangular tube; styles 3; stigmas penicillate. Fr. a trigonous nut included in the hard accrescent perianth, the 3 outer segments of which are spine-tipped.

Perennial or sometimes annual herbs, occasionally climbing, rarely shrubby; roots often thick. Lvs radical or cauline, very variable, mostly longer than wide, commonly bullate and undulate, sometimes hastate; ochreae ± tubular. Fls in simple or branched racemes or spikes, often strongly protandrous, often whorled, green, often turning reddish later, mostly ☿, sometimes unisexual (plants monoecious or dioecious). Pedicels jointed, usually deflexed at fruiting. Perianth segments 6, ± free; outer 3 remaining small and thin and often reflexing; inner 3 (fr. valves) enlarging in fr., often becoming hard, prominently veined, not keeled, sometimes with marginal teeth, sometimes with dorsal tubercles, these forming enlarged corky areas on the midrib. Stamens 6, in 2 whorls. Styles 3, very short; stigmas usually strongly lobed and mostly penicillate. Fr. a trigonous nut, with surrounding perianth segments sometimes spiny.