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. <u>Margins</u> entire. Margins entire. Veins 3, greatest distance between lateral veins near or proximal to middle. <b>Stipules</b> absent. 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. <b>Calyx</b> absent. <b>Corolla</b> (petals) absent. Stamens 2, 4-locular. <b>Ovary</b> 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.