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Slender Pondweeds comparison table
Slender Pondweeds comparison table

Potamogeton gramineus, Potamogeton berchtoldii, Potamogeton gemmiparus


NOTE: Recent DNA evidence has identified three distinct species of slender pondweed occurring in Maine: P. gemmiparus (previously P. pusillus var. gemmiparus), P. pusillus (previously P. pusillus var. pusillus), and P. berchtoldii (previously P. pusillus var. tenuissimus). The description that follows has been generalized to pertain to all three species.

Slender pondweed in-situ
Slender pondweed in-situ

Habitat: Slender pondweeds grow in the submersed plant community. They are found in soft sediments in quiet water of lakes, ponds and slow-moving streams, in depth up to three meters. These pondweeds thrive in deeper, darker water and will tolerate turbid and brackish conditions.

Description: Slender pondweeds have submersed leaves only. Sinuous stems (up to 1.5 meters long) emerge from delicate roots. Stems may be round to slightly compressed in cross section, and often branch repeatedly near the growing tips. Narrow leaves (1 to 7 cm long and 0.2 to 2.5 mm wide) are entire, alternately arranged in a spiral, and attach directly to the stems at their base (no petioles). A pair of tiny bumps (actually glands) occur at the nodes, one on each side of the base of the leaf. (Not every node has well-developed glands, so you may need to check several.) The leaves have one to three veins, and the mid-vein may be bordered by one or more light-colored, translucent bands of air-filled cells called lacunae. Leaves taper slightly toward the base; the tips of the leaves are varied depending on sub-species, and may be blunt or sharply pointed. Flimsy, tube-like stipules may occur around the stems, but they are fairly inconspicuous, and are not always persistent. Flowers, followed by tiny fruits, occur in whorls on slender spikes (0.5 to 6 cm long). The spikes grow from stem and leaf axils and may be submersed or emergent. The plump fruits are asymmetrical but somewhat rounded to oval in shape, with a short protrusion (called a beak) at one end. Numerous winter buds (or turions) are produced in the leaf axils toward the end of the growing season. The buds are elongated (1 to 3 cm long), generally dark in color, resembling tiny, partially-unhusked corn cobs. (A hand lens is helpful when observing lacunae, leaf glands, stipules, fruits, and winter buds.) Slender pondweeds are generally light green to olive green (occasionally reddish) in color

slender pondweed fruits
The fruits are rounded to oval with a short beak

U.S. Range: Slender pondweeds are native to Maine and New England. The range of P. gemmiparus is limited to New England. The other two sub-species occur throughout most of the United States. P. pusillus and P. berchtoldii are both known to hybridize with another native pondweed species. Populations of these hybrid pondweeds occur in Maine.

slender pondweed winter bud
Slender pondweed winter bud (turion)

Annual Cycle: Slender pondweeds are aquatic perennials that propagate by spreading roots, winter buds and, to a more limited degree, seeds. Flowers occur in the spring. Fruits and winter buds mature by early to mid-summer. Plants often die-back to their roots before the end of the growing season, depositing winter buds and seeds on the sediments. New growth sprouts from the roots, buds and seeds as the water begins to warm in the spring.

Value to the Aquatic Community: Slender pondweeds are an important food source for a variety of waterfowl. The fine-leaved plants often form extensive beds, providing food and cover for fish and their fry. Muskrat, deer, beaver and moose are all known to feed upon this plant.

Look Alikes: Submersed leaves of slender pondweeds may be confused with other narrow-leaved species of the Potamogeton genus, European naiad, Slender naiad, threadlike naiad, and some Stoneworts.

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Slender pondweed in-situ Slender pondweed seed Slender pondweed specimen Slender pondweed winter bud (turion) Slender pondweed illustration

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