Description

Key Characters:

Growth Form: Aquatic perennial herbs.

Stems: Stems prostrate to ascending or erect, often rooting at the lower nodes.

Roots:

Leaves: Leaves simple. Usually whorled. Submerged parts pinnatifid, the segments capillary. Margins entire, toothed, or deeply dissected. Petiolate or sessile. Stipules absent.

Flowers: Flowers sessile, usually in the axils of the upper, reduced leaves, usually above the surface of the water, each flower often subtended by persistent or deciduous bracteoles. Flowers unisexual, uppermost usually staminate, lower ones pistillate. Calyx of staminate flowers with (2)4-lobes; Calyx of pistillate flowers with 4 teeth. Corolla of staminate flowers with petals (0)2–4; pistillate flowers with corolla (petals) absent. Stamens in staminate flowers 2, 4, or 8; anthers tetrathecal, opening by slits. Ovary inferior (pistillate flowers), 4-celled; ovules anatropous, pendulous from apex; styles as many as sepals, rarely half as many, feathery; stigmas 4, recurved and plumose.

Fruit: Fruit separating into 4 nut-like segments at maturity; these sometimes tuberculate on the back; the sepals persistent on the fruit; erect or reflexed. Seeds 1–4; endosperm copious; fleshy and oily.

Ploidy:

Habitat:

Elevation Range: