Stems freely branching proximally to distally, terete, 20--50(--70) cm. Leaves: length and width of those on main stem only slightly larger than those on branches; stipules with stipular sheaths inflated 3--5 times stem thickness, 2--9 cm, ligule absent, obscure, or to 0.2 mm; blade narrowly filiform to linear, 1--10(--15) cm ´ 0.2--2.9 mm, apex rounded, obtuse, or slightly notched; veins 1(--3). Inflorescences: peduncles terminal, erect, slender, 3--15 cm; spikes moniliform, 10--80 mm; verticels 3--12. Fruits brown, obliquely obovoid, 3--3.8 mm ´ 2--2.9 mm; beak inconspicuous. 2n = 78.

Flowering late summer--fall. Deep lakes and ponds; 0--2300 m; Alta., B.C., Man., N.W.T., Nunavut, Ont., Que., Sask., Yukon; Alaska, Colo., Idaho, Minn., Mont., N.Dak., Oreg., S.Dak., Utah, Wash., Wis., Wyo.; Eurasia.

One hybrid, P. pectinatus ´ P. vaginatus (= P. ´ bottnicus Hagström), with this species as a putative parent has been described under the genus Potamogeton.

OTHER REFERENCES Correll, D. S. and M. C. Johnston. 1970. Manual of the Vascular Plants of Texas. Renner, Tex. Harada, I. 1956. Cytological studies in Helobiae. I. Chromosome idiograms and a list of chromosome numbers in several families. Cytologia 21: 306--328. Hellquist, C. B., C. T. Philbrick, and R. L. Hilton. 1988. The taxonomic status of Potamogeton lateralis Morong (Potamogetonaceae). Rhodora. 90: 15--20. Hindáková, M. and T. Schwarzová. 1980. Pp. 728--730. In: Á. Löve. IOPB Cchromosome number reports LXIX. Taxon 29: 703--730. Jøörgensen, C. A., T. H. Søörensen, and M. Westergaard. 1958. The flowering plants of Greenland. A taxonomical and cytological survey. Kongel. Danske Vidensk.-Selsk.Biol. Skr. 9(4): 1--172. Löve, Á. 1954. Cytotaxonomical evaluation of corresponding taxa. Vegetatio 5--6: 212--224. Löve, Á. and D. Löve. 1981. Pp. 699--701. In: Á. Löve.IOPB Cchromosome number reports LXXII. Taxon 30: 694--708. Moore, E. 1913. The potamogetons in relation to pond culture. Bull. U.S. Bur. Fish. 33: 251--291. Palmgren, O. 1939. Cytological studies in Potamogeton. Bot. Not. 1939: 246--248. Preston, C. D. 1995. Pondweeds of Great Britain and Ireland. London. Stern, K. R. 1961b. Chromosome numbers in nine taxa of Potamogeton. Bull. Torrey Bot. Club 88: 411--414. Taylor, R. L. and G. A. Mulligan. 1968. Flora of the Queen Charlotte Islands. Part. 2. Cytological Aspects of the Vascular Plants. Ottawa.