Description

Key Characters:

Growth Form: Floating aquatic herb.

Stems: Stipes small, white, often decaying.

Roots: Roots to 3 cm; tip usually sharp pointed; sheath winged at base (wing 1–2.5 times as long as wide).

Leaves: Leaves absent. Fronds floating, 1 or 2–few, coherent in groups, 1 often very distinct papilla near apex on upper surface and 1 above node; anthocyanin absent, no reddish color; largest air spaces much shorter than 0.3 mm; distinct turions absent. Fronds ovate–lanceolate, flat, 1–6 mm, 1–3 times as long as wide. Margins entire. Veins 3, greatest distance between lateral veins near or proximal to middle. Stipules absent.

Flowers: Flowers borne in a pouch, 2 staminate and 1 pistillate, enclosed in a membranous sheath in a marginal cleft of the frond, opening along the side or nearly closed. Flowers unisexual, 1(--2) per frond, surrounded by small utricular, membranous scale. Calyx absent. Corolla (petals) absent. Stamens 2, 4-locular. Ovary superior; ovaries 1–ovulate, utricular scale open on 1 side.

Fruit: Fruit 0.5–0.8 mm; not winged. Seeds with 8–26 distinct ribs; falling out of fruit wall after ripening.

Ploidy: 2n = 40; 42; 50; 60; 80; 84

Habitat: Mesotrophic to eutrophic; quiet waters in warm–temperate to tropical regions.

Elevation Range: 0–1,300 m.