Sheathed Pondweed

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

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.

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.

Flowering late summer--fall.

Deep lakes and ponds; 0--2300m.

Potamogeton vaginatus Turczaninow, Bull. Soc. Imp. Naturalistes Moscou 27(2): 66--67. 1854