Perennial, aquatic herb from long rhizomes; stems 10-100 cm long, up to 1 mm in diameter, profusely branched at the base.
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.
Inflorescence spikelike, the spikes 1.5-2.5 cm long, interrupted, with 2-8 whorls of flowers, the stalks thin.
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.
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
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