Potamogeton crispus L.: Curlyleaf pondweed, crisp pondweed. Potamogetonaceae (pondweed family). Non-native perennial. This submersed plant has rooting rhizomes and stolons and lacks floating leaves; it can grow in water to 15 ft (4.5 m). Reproduction is from rhizomes and stiff, hard winter buds. Stems are pale, with reddish nodes, flat, and often angled back and forth in a zig-zag pattern. There is frequent branching and high leaf density. The alternate leaves are attached directly to the stem without stalks. They are firm, 1.2 - 4.75 in (3 - 12 cm) long, narrowly rectangular to 0.6 in (1.5 cm) wide, with rounded to broadly-pointed tips and conspicuously toothed and wavy margins. The prominent midrib is often pale to reddish. Short flower spikes are on a stalk that may curve as seeds ripen. The compact, thickened buds, or turions, are armed with stout spiky teeth on the margins of their compressed leaves. They provide efficient reproduction, but once they have fallen to the substrate are a nuisance to swimmers. This plant spreads aggressively within a season and increases its range from year to year, eliminating native vegetation. Its extremely dense stands can impair fishing, swimming and all other water uses.