1. Najas L. (naiad, water nymph)

(Haynes, 1979)

Plants annual, monoecious (dioecious elsewhere). Stems diffuse, highly branching, rooting at the lower nodes. Leaves opposite or appearing whorled, filiform, the margins serrulate, sometimes obscurely so. Stipules fused to the leaf base, membranous, sheathing. Flowers 1–3 per leaf axil, minute, unisexual. Perianth reduced to 2 minute, membranous scales or usually absent in pistillate flowers. Staminate flowers with 1 stamen. Pistillate flowers with 1 pistil. Pistils with 1 locule and 1 short style that branches into 2–4 narrowly triangular branches. Fruits 1‑seeded, the outer coat very thin and more or less transparent, wearing away irregularly. Seeds narrowly elliptic to obovate, sometimes curved at the tip, the hard surface variously ornamented. Thirty‑five to 40 species, worldwide.

The species of Najas are important food for waterfowl, and the often dense mats formed by most species provide cover for young fish and other aquatic organisms.