Callitriche heterophylla Pursh

Monoecious aquatic herb with long ascending stems, little branched, often with floating rosettes. Lvs very variable but submerged lvs often linear-elliptic, 1-nerved, shallowly 2-toothed; aerial lvs usually obovate, 3–7-nerved; free veins 0; lvs of plants on mud oblong. Fls 1 ♂ and 1 ♀ together in each axil. Bracteoles white, conspicuous, persistent. Filaments to 4 mm long; anthers c. 0.2 × c. 0.3 mm. Styles 1–6 mm long, persistent or caducous. Fr. sessile, (0.6)–0.7–0.8–(1) mm long, suborbicular; mericarp faces convex; wing narrow, usually only at top of mericarp, sometimes 0; commissural groove very shallow and narrow.

[From: Webb et al. (1988) Flora of New Zealand. Volume 4.]