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Potamogeton alpinus


Red pondweed in-situ
Red pondweed in-situ

Habitat: Red pondweed grows in the submersed plant community. It is found in cold water of lakes and streams.

Description: Red pondweed has two distinct leaf types: submersed leaves and floating leaves. The leaves are oval to oblong, 4 to 25 cm long, tapering to a blunt or slightly acute tip. The leaves are alternately arranged on unbranched stems and attached directly to the stems at the base. Each leaf has 7 to 9 lengthwise veins; the prominent veins generally alternately with faint ones. It is common for the submersed leaves to have a distinctly red tinge, especially when dried. The floating leaves are slightly smaller and delicate, with rounded tips and margins tapering gradually to the petiole. The stems are round in cross-section. The flowers, followed by fruit, occur among the floating leaves and are densely arranged on an emergent spike. The plump fruits have a small stalk protruding from the rim at one end, and a curved beak protruding from the other. The bulging sides are smooth with slight depressions along the middle.

Variable Milfoil Range Map
U.S. range map of variable water-milfol

U.S. Range: Red pondweed is native to Maine, New England and much of the northern and western United States. Two varieties of red pondweed have been documented in the US (var. tenuifolius and subellipticus), primarily based upon the submersed leaf shape. However, since both leaf types may be observed in the same population, the distinction is rarely recognized.

Annual Cycle: Red pondweed is an aquatic perennial that propagates from seeds and creeping rhizomes. Plants die-back to the rhizome as winter sets in. New growth sprouts from seeds and rhizomes when the water begins to warm in the spring. Flowers appear by mid-summer, and fruit matures by late summer. Hybrids with another native Maine pondweed, Potamogeton gramineus, occur in Maine.

Value to the Aquatic Community: The leaves of P. alpinus offer shade, shelter and foraging opportunities for fish. Fruits are a valuable food for waterfowl.

Look Alikes: May be confused with other specieso f the Potamogeton genus including curly-leaf pondweed. Red pondweed is most often confused with variable pondweed (Potamogeton gramineus), but P. gramineus has branching stems and finely serrated margins under magnification.

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Red pondweed specimen Red pondweed submersed leaves Red pondweed range map Red pondweed illustration Red pondweed illustration Red pondweed fruit

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