Potamogeton crispus is a submerged perennial monocotyledon herb, with a winter annual-like life-cycle, from corm-like, aestivating apical buds (turions) that germinate in Autumn (late Sept.), leafy stems, rooted in substrate, produced in fall-winter, dying back to dormant, hard, scaly-thorny apices in late Spring-early Summer. These sink to the bottom of the water-body and lie dormant during Summer; leafy stems slender, compressed, simple or sparsely branched.
Leaves alternate, ranked along stem, leaves of winter and early spring narrow, flat-margined with a pointed tip; early summer leaves oblong, strap-like, to 8 cm long, 1.5 cm wide, tip blunt, base narrowed, sessile, margin regularly undulate, finely toothed, midrib reddish, conspicuous, marginal vein extends around edge of leaf.
Flowers reddish-brown, minute, regular, inflorescence of spikes 1-2 cm long that extend above the water surface; blooming May-June, wind pollinated.
Fruit 0.3 cm long, with a beak 0.2-0.3 cm long 1-seeded; fruiting June-July, probably dispersed by water or ducks, Germination apparently infrequent. Aestivating buds produced along leafy stem. When mature they drop off and the rest of the plant dies, July-Aug. Seeds and foliage eaten by ducks. Foliage high in nitrogen (Catling and Dobson 1985).
Wetland status: OBL.
Frequency in NYC: Apparently very infrequent but probably not well inventoried.
Habitat: Shallow, high nutrient, alkaline, polluted water, typical of many artificial, urban ponds; Tolerant of slightly brackish water. Found almost always in water with high nitrate (2-24 mg/L)*, phosphate (0.2-1.12 mg/L)* and pH 6.7-9.8*.
Notes: Very aggressive, tends to grow above native aquatics, shading them severely. Foliage dies off in mid-summer, avoiding competition with other aquatic herbs. Decomposition adds to oxygen deficit of shallow water bodies in Summer. Leafy plants can overwinter under ice and snow of pond surface. Attacked by few, if any, insects or diseases (Catling and Dobson 1985). May be introduced into wetland mitigations with nursery stock from contaminated ponds.
* Unpolluted water has levels of Nitrate below 1 mg/L, Phosphate below 0.1 mg/L, pH 6.5-8. (Mayio 1997).