1. Najas L. (naiad, water nymph)
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 of Najas are important food for waterfowl, and the often dense
mats formed by most species provide cover for young fish and other aquatic