General:
Perennial, aquatic herb from strong rhizomes; stems mostly unbranched or sparingly branched, with a reddish tinge, nearly circular in cross-section, tapered, up to 200 cm long.

Leaves:
Submersed leaves flat, thin, linear-lanceolate, 4-10 cm long, 5-20 mm wide, with 7 to 9 veins, unstalked, not clasping the stem, the stipules 1.5-2.5 cm long, thin, membranous, persistent; floating leaves, if developed, lanceolate, 3-8 cm long, 2-5 cm wide, gradually tapered into stalks.

Flowers:
Inflorescence spikelike, the spikes 1-3.5 mm long, with 5 to 10 whorls of flowers, the stalks thick.

Fruits:
Achenes, egg-shaped, 3-3.5 mm long, 2-2.4 mm wide, slightly compressed at their sides, the beaks long, often curved, the dorsal keels narrow, prominent, the lateral keels obscure.

Notes:
Stem anatomical characters Interlacunar and subepidermal bundles lacking, pseudohypodermis lacking, endodermis of O-cells.

Source:  The Illustrated Flora of British Columbia

If more than one illustration is available for a species (e.g., separate illustrations were provided for two subspecies) then links to the separate images will be provided below. Note that individual subspecies or varietal illustrations are not always available.

Illustration Source:  The Illustrated Flora of British Columbia

Synonyms and Alternate Names:
Potamogeton alpinus subsp. tenuifolius (Raf.) Hultén
Potamogeton alpinus var. subellipticus (Fernald) Ogden
Potamogeton alpinus var. tenuifolius (Raf.) Ogden
Potamogeton tenuifolius