Callitriche heterophylla is an annual herb, small aquatic or rooted in mud, to 20 cm long, rooting from lower nodes, often in dense patches, stems thread-like, compressed.
Leaves opposite, those below water linear, to 1.5 cm long, leaves above water spatulate, crowded into a small rosette at stem tips, margins entire.
Flowers (use hand lens) in leaf axils, 1 stamen, one 4-lobed ovary, with two stigmas, tiny, whitish fleshy bracts from base of female flower, found flowering late May.
Fruit to 0.1 or slightly less, flattened, margins rounded, very shallowly or not at all grooved; April-Dec.
Wetland status: OBL.
Frequency in NYC: Very infrequent.
Habitat: Shallow, still water or on mud.
Notes: Plants eaten by muskrats. Very similar to C. palustris but usually darker green, fruit never winged.