General: Perennial, aquatic herb from long rhizomes; stems up to 120 cm long, 1-3 mm wide, unbranched or sparsely branched.
Leaves: All submersed, linear, thread-like, 5-10 cm long, the lower ones up to 3 mm wide, with 1 vein, the tips round to blunt or notched, firm, dark green, the stipules 2-5 cm long, fused into inflated sheaths, the leaf blades arising close to the tips of the sheaths.
Flowers: Inflorescence spikelike, the spikes 1.5-7 cm long, interrupted, with 3 to 12 whorls of flowers, the stalks thin.
Fruits: Achenes, almost globe-shaped, 3.5-4 mm long, 2.5-3 mm wide, widest above the middle, the beaks and keels absent, the surface with fine, ray-like grooves.
Notes: Many specimens in herbaria identified as Stuckenia vaginata (Potamogeton vaginatus) are, in fact, misidentified specimens of Stuckenia filiformis ssp. occidentalis.
Lakes in the montane zone; rare in BC E of the Coast-Cascades Mountains; circumpolar, N to AK, YT and NT, E to NF and S to ME, OH, MI, WI, MN, SD, CO, ID and OR; Eurasia.