Potamogeton perfoliatus and Potamogeton richardsonii
NATIVE TO MAINE
Two Potamogeton species found in Maine share the common name “clasping-leaf pondweed”: Potamogeton perfoliatus and Potamogeton richardsonii. Of the two species, ,P. perfoliatus is more common in Maine. Alternative common names for both species do exist, but are less frequently used. Potamogeton perfoliatus is also called perfoliate pondweed and P. richardsonii is also called red-head pondweed.
Description: Both species have long, branching stems that are rounded in cross-section (1 to 2.5 mm in diameter), emerging from a spreading rhizome. The submerged leaves are alternately arranged, oval to lance-shaped, and clasp the stem with a lobed base. No floating leaves are produced. Fruiting stalks emerge from leaf axils toward the end of the growing season. Clusters of small fruits form in a spike toward the tip. Each fruit is disk-like with an erect beak-like.
The leaves help to distinguish the two species. The leaves of P. richardsonii are 3 to 12 cm long with wavy edges, and 13 to 21 veins (some more prominent than others). The more fibrous portions of the stipules persist in the leaf axils, leaving stiff tufts. The bases of the leaves clasp one-half to threequarters of the way around the stem. The leaves of P. perfoliatus are generally smaller (1 to 5 cm long) with 7 to 15 veins. The stipules (which only occur on the upper portion of the stem) disintegrate without a trace fairly early in the growing season. The leaf bases clasp all of the way around the stem.
U.S. Range: Both claspingleaf pondweeds are native to Maine, New England and other parts of the United States. (P. perfoliatus is more common in Maine.) The two species are known to hybridize with each other, and P. perfoliatus hybridizes with two other pondweed species as well. All three hybrids occur in Maine.
Annual Cycle: Clasping-leaf pondweeds are perennials that propagate by spreading rhizomes, and, when conditions are favorable, from seed. Flowers, followed by fruits, appear by mid-summer. Plants die back to their rhizomes at the end of the growing season. New growth emerges from rhizomes and seeds when the water begins to warm in the spring.
Value to the Aquatic Community: The fruits of clasping-leaf pondweeds provide food for ducks and geese. The plants are grazed by muskrat, deer, beaver and moose. The leaves and stems are colonized by macroinvertebrates and provide shelter and foraging opportunities for fish.
Look Alikes: May be confused with other species of the Potamogeton genus, including curly-leaf pondweed.
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