Stems: glands common, to 0.5 mm diam. Leaves: stipules brown or rarely white, fibrous, shredding at tip, veins in age remaining as fibers. Inflorescences: spikes interrupted. Fruits pale -green, 1.4--1.7 ´ 1.1--1.2 mm; keel less than or equal to 0.2 mm high; beak less than or equal to 0.2 mm. Chromosome number unknownnot available. Flowering and fruiting summer--fall. Warm waters of shallow lakes, springs, streams, and rivers; of conservation concern; 600--2700 m; Calif., Idaho, Oreg., Utah, Wash., Wyo. Potammogeton foliosus subsp. fibrillosus is known from the warm waters of the northwestern United States. It differs from subsp. foliosus by the stipular tissue between the veins decomposing, leaving only strands formed by the fibrous veins. In addition, nodal glands are quite common.