Potamogeton spirillus is a perennial, submerged monocotyledon, rooted aquatic, stems to 1.5 m long, bushy-branched or elongate.
Leaves alternate, submerged leaves linear, 1-8 cm long, to 0.2 cm wide, 1-3 veined, tip usually blunt; floating leaves, when present, usually oval, 0.7-3.5 cm long, 0.2-1.3 cm wide, veins 5-13.
Flowers minute in spikes; submerged spikes round, with 1-8 fruits on curved-back stalks to 0.3 cm long; aerial spikes cylindrical to 1.3 cm long with 4-35 fruits.
Fruit about 0.2 cm long sharply keeled on back, with a coiled pattern on sides and depressed center (shape of embryo); blooming and fruiting July-Nov. (Hough 1983).
Wetland status: OBL.
Frequency in NYC: Very infrequent.
Habitat: Quiet water.