General:
Perennial, aquatic herb from long rhizomes; stems 10-100 cm long, up to 1 mm in diameter, profusely branched at the base.

Leaves:
All submersed, linear, thread-like, 5-10 cm long, 0.2-1.5 mm wide, with 1 vein, thin, green, the tips rounded to blunt, the stipules 0.5-1 cm long, fused, forming a tight sheath around the stem, the leaf blades arising close to the tips of the sheaths.

Flowers:
Inflorescence spikelike, the spikes 1.5-2.5 cm long, interrupted, with 2-8 whorls of flowers, the stalks thin.

Fruits:
Achenes, almost globe-shaped, 2-3 mm long, 1.5-2.4 mm wide, widest above the middle, the beaks and keels absent, the surface with fine, ray-like grooves.

Notes:
Two subspecies occur in British Columbia. In addition, a third one (ssp. filiformis) can be expected in N BC.

1. Stems 20-100 cm long; stipules inflated at the base, especially in the leaves lower on the stem, disintegrated with age....................ssp. occidentalis (J.W. Robbins) Haynes, D.H. Les, & M. Kral

1. Stems 10-30 cm long; stipules tightly clasping the stem, persistent.

2. Flowers and fruits in whorls less than 4 cm apart; leaves 0.5-1 mm wide....................ssp. alpina (J.W. Robbins) Haynes, D.H. Les, & M. Kral

2. Flowers and fruits in whorls 4 cm or more apart; leaves 0.2-0.5 mm wide....................ssp. filiformis

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:
Coleogeton filiformis subsp. occidentalis (J.W. Robbins) D.H. Les & Haynes
Potamogeton filiformis var. occidentalis (J.W. Robbins) Morong
Potamogeton interior Rydb.
Stuckenia filiformis var. occidentalis (J.W. Robbins) Dorn