Spiral Pondweed (Potamogeton spirillus)
Updated: Jun 16, 2021
Spiral pondweed has submersed and floating leaves, though floating leaves are typically few or may be absent.
Floating leaves are firm, green, oval-elliptic, less than 1½ inches long, up to ½ inch wide, toothless, rounded to bluntly pointed at the tip, rounded to tapering at the base, on a stalk shorter than the blade. Blades have 5 to 15 veins.
Submersed leaves are more or less spirally arranged, green to reddish, linear and thread-like, often arching or coiled, up to 3 inches long, .5 to 2 mm wide, bluntly to sharply pointed at the tip, stalkless, and have 1 to 3 veins. Stems are flattened and branched. Colonies are often formed from spreading rhizomes. (Source: https://www.minnesotawildflowers.info/aquatic/spiral-pondweed).
Look-alikes - Spiral pondweed is similar to native waterweed but can be distinguished by a) presence of small elliptical floating leaves on spiral pondweed vs none on waterweed and b) attachment of leaves to the stem - spiral pondweed leaves alternate on the stem whereas they occur in whorls on waterweed.
Spiral pondweed in Heron Cove (Zone 1 - note both small elliptical floating leaves and thin thread-like submerged leaves. Photo by Don Yurewicz