Page author: Don Knoke
Potamogeton gramineus
grassy pondweed, variable pondweed

Distribution: Alaska to Maine, south to California and New Mexico in the west and West Virginia in eastern United states

Habitat: Standing or running water

Flowers: June - August

Origin: Native

Growth Duration: Perennial

Conservation Status: Not of concern


Aquatic, herbaceous perennials from slender rhizomes, the slender stems freely branching, sub-terete, up to 2 m. long.


Leaves alternate, the submersed leaves sessile, linear to lanceolate or oblanceolate, 3-9 cm. long and 3-10 mm. broad, 3- to 7-nerved; floating leaves long-petiolate, elliptic to oblong-elliptic, 2-5 cm. long and 1-2 cm. broad, 13- to 19-nerved; stipules open, firm, up to 3 cm. long.


Flowers perfect, in 6-10 crowded whorls, in spikes 1.5-2.5 cm. long on peduncles 4-10 cm. long, stout, thickened upward; perianth of 4 clawed segments, each with an upturned, oval blade; stamens 4, fused with the claws; pistils 4, sessile.


Achenes obliquely obovoid, 2-2.8 mm. long including the short stylar beak, the dorsal keel well developed, the lateral ones obscure.

Accepted Name:
Potamogeton gramineus L.
Publication: Sp. Pl. 1: 127. 1753 (as gramineum). 1753.

Synonyms & Misapplications:
Potamogeton gramineus L. var. maximus Morong [VPPNW1]
Potamogeton gramineus L. var. myriophyllus J.W. Robbins [IMF6]
Potamogeton heterophyllus Schreb.
Additional Resources:

PNW Herbaria: Specimen records of Potamogeton gramineus in the Consortium of Pacific Northwest Herbaria database.

WA Flora Checklist: Potamogeton gramineus checklist entry.

E-Flora BC: Potamogeton gramineus atlas page.

CalPhotos: Potamogeton gramineus photos.

USDA Plants: Potamogeton gramineus information.

7 photographs:
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