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.

Perennial submersed aquatic herb with rhizomes 20 cm - 0.5 m tall

Stem: freely branched.

Leaves: submersed, alternate, stalkless, opaque, 1 - 10 cm long, to 3 mm wide, thread-like to linear with a tapering base and blunt, rounded, or slightly notched tip, typically one-veined, channeled, plump. Stipules adhered to base of leaf blade for two-thirds or more their length, 2 - 9 cm long, sheaths inflated three to five times the width of the stem.

Inflorescence: an upright, bead-like spike with three to twelve whorls of flowers, submersed, 1 - 8 cm long, on a terminal stalk. Stalk slender, 3 - 15 cm long, flexible.

Flowers: greenish, tiny. Stamens four. Anthers two-chambered, with four edge-to-edge sepal-like outgrowths. Pistils four.

Fruit: an achene, brown, 3 - 3.8 mm long, 2 - 3 mm wide, obliquely reverse egg-shaped, plump, with an inconspicuous beak.

Similar species: Pondweeds in the genus Potamogeton are similar to those of Stuckenia, but the submersed leaves of Potamogeton are translucent, flat, and lack channels, whereas those of Stuckenia are opaque, channeled, and plump. Compare the inflated stipule sheaths of this species with S. pectinatus to best distinguish between the two.

Habitat and ecology: Rare in the Chicago Region. A single specimen was collected just offshore of a lake in Cook County, Illinois.

Occurence in the Chicago region: native

Etymology: Vaginatus means "with a sheath."

Author: The Morton Arboretum

Much like no. 1 [Potamogeton filiformis Pers.], avg coarser; tubers 3-5 cm; lvs 1-2 mm wide; stipular sheaths (at least of the primary lvs) subinflated, 2-3 times as thick as the stem, 2-5 cm, open to the base; spike with 5-12 nearly equidistant whorls of fls, 3-8 cm at maturity; fr 3-3.5 mm; 2n=78. Deep, alkaline or brackish waters; circumboreal, in Amer. s. to N.J., Mich., N.D., and Utah.

Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.

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