Description

Key Characters:

Growth Form: Aquatic or semiaquatic, glabrous annual or perennial herbs.

Stems: Typically with creeping rhizomes or stolons, sap milky.

Roots: Fibrous root system.

Leaves: Leaves simple. Alternate, crowded into a basal rosette; leaves two-ranked or spiral, usually with distinct petiole and blade. Blades sagittate to hastate or elliptic, or not well–developed (usually immersed forms). Primary veins parallel from base of blade to apex, secondary veins reticulate. Petioles flattened, forming a linear, leaf, petioles of well–developed leaves open and sheathing, ligules absent. Stipules absent.

Flowers: Flowers in umbellate, racemose, or paniculate inflorescences, each flower subtended by a bract; inflorescence branches whorled. Flowers bisexual (perfect) or unisexual (and then plants monoecious, with lower flowers pistillate and upper ones staminate, or occasionally dioecious), or sometimes with bisexual (perfect) and unisexual flowers mixed and then upper ones usually staminate, actinomorphic. Calyx of 3 sepals, imbricate. Corolla of 3 petals, usually white, caducous, rarely absent. Stamens (3)6 to numerous, when 6, arranged in a single whorl, 1 pair opposite each petal. when numerous, appearing spirally arranged; filaments distinct; anthers 2-loculed, dehiscing longitudinally. Ovary superior, 3 or 6 to numerous, in whorls, arranged in a ring, or crowded into head-like clusters; ovules 1-2, restricted to base of pistil, anatropous or amphitropous; style terminal or basilateral; stigma often decurrent.

Fruit: Achenes or occasionally a basal dehiscent follicle. Seeds without endosperm; embryo U-shaped.

Ploidy:

Habitat: Aquatic or semiaquatic.

Elevation Range: