Hermaphroditic (or rarely dioecious), unarmed, glabrous or pubescent, terrestrial or aquatic, low annual or perennial herbs. Stems branched, erect to prostrate and often rooting at the nodes, leptocaulous. Leaves alternate, petiolate, the bases stipulate but not sheathing; blades simple (and often peltate and orbicular) to palmately lobed or compound with ovate or obovate lobes or sessile leaflets; membranaceous, the margins entire to crennate or dentate. Inflorescences axillary, erect or lax, often simple umbellate but sometimes compound umbellate or forming continuous to interrupted spikes; bracts present or lacking; pedicels short and stout to long and slender, unarticulated. Calyx minute to lacking; petals 5, valvate, free; stamens 5; carpels 2, ovaries inferior, styles free or basally connate; the disc conical to depressed. Fruits dry schizocarps (lacking carpophores), usually 5-ribbed, glabrous to pubescent or spinose, orbicular to ellipsoid, flattened laterally; endocarp sclerified. 2n = 18, 24, 32, 36, 48, 60, 72, 96, 132, 144, 162, 184.