Description

Key Characters:

Growth Form: Floating aquatic herb.

Stems: Stipes white, small, often decaying.

Roots: Roots to 15 cm, tip mostly rounded; sheath not winged.

Leaves: Leaves absent. Fronds floating, 1 or 2–5 or more, coherent in groups, very distinct papillae near apex, some smaller indistinct ones on midline of upper surface; lower surface very often red colored (more intensely than on upper), coloring beginning at attachment point of root, lower upper surface sometimes with red spots; air spaces shorter than 0.3 mm; distinct turions absent. Fronds obovate, flat or gibbous, 1–3.5 mm, 1–1.5 times as long as wide. Margins entire. Veins 3, greatest distance between lateral veins near 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 with narrow opening at apex.

Fruit: Fruit 0.5–0.7 mm; not winged. Seeds with 10–16 distinct ribs; staying within fruit wall after ripening.

Ploidy: 2n = 40; 42; 50

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

Elevation Range: 0–800 m.