Vallisneria

Plants perennial, of fresh or brackish waters. Rhizomes and stolons present. Erect stems rooted in substrate, unbranched, short. Leaves basal, submersed, sessile; blade linear, base grading into sheath, apex obtuse to apiculate; midvein with 4–5 rows of lacunae on each side, balde appearing 3-zoned with light-colored middle zone bordered on each side by darker zone; abaxial surfacely without prickles or aerenchyma; intravaginal squamules entire. Inflorescences cymose, long-pedunculate; spathe not winged. Flowers unisexual, staminate and pistillate on different plants, submersed or floating, sessile (staminate) or pedicellate (pistillate); petals transparent. Staminate flowers: filaments distinct, released from spathe and floating to surface; anthers spheric; pollen in monads. Pistillate flowers floating; ovary 1-locular; styles 1, not 2-fid. Fruits cylindric to ellipsoid, ridged, dehiscing irregularly. Seeds ellipsoid, glabrous.

Distribution

North America, South America, Eurasia, Africa, Australia.

Discussion

Vallisneria is generally considered to have 1-flowered pistillate inflorescences. A few populations in southern United States and Central America, however, have cymes with up to 30 flowers. The United States populations include those in Florida, Alabama, and Mississippi.

Species 26 (1 in the flora).