Leaves: stipules connate; blade 1.4--6.5 cm ´ 0.5--1.9 mm, apex acute or rarely apiculate, rarely with bristle, lacunae present or absent, 0--2 rows each side of midrib; veins 1--3. Inflorescences: peduncles 1--3 per plant, filiform to cylindric; spikes cylindric, interrupted. Fruits obovoid, sides centrally concave; beak toward adaxial edge, rarely median. 2n = 26 (Eurasia).

Flowering and fruiting spring--fall. Streams, lakes, or marshes; 0--3300 m; Alta., B.C., Man., N.B., N.W.T., N.S., Ont., P.E.I., Que., Sask., Yukon; Ala., Ariz., Ark., Calif., Colo., Conn., Del., D.C., Fla., Ga., Idaho, Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Mont., Nebr., Nev., N.H., N.J., N.Mex., N.Y., N.C., N.Dak., Ohio, Okla., Oreg., Pa., R.I., S.C., S.Dak., Tenn., Tex., Utah, Vt., Va., Wash., W.Va., Wis., Wyo.; South America; Eurasia; Africa.

Potamogeton pusillus subsp. pusillus is nearly worldwide. When it is in fruit, the inflorescence is interrupted. That character combined with its narrow, linear, 1--3-veined leaves makes this taxon easily recognized. The nodal glands are green, essentially the color of the stems. Often appearing only as bumps on the stem at the nodes, they are difficult to see. Also, because the glands frequently occur at only a few nodes per plant, one can easily overlook them.

Perennial submersed aquatic herb 18 cm - 1.5 m tall

Stem: very slender, much-branched above, jointed, with or without nodal glands. Glands green, to 0.5 mm wide, appearing as small bumps.

Leaves: submersed, more or less arranged spirally, stalkless, translucent, pale green to olive green, sometimes slightly reddish, 1.4 - 6.5 cm long, 0.5 - 1.9 mm wide, narrowly linear with a slightly tapering base and pointed tip, one- to three-veined. Stipules axillary, free from leaf blade, brown to green or white, to 1 cm long, with fused margins.

Inflorescence: an upright, cylindrical spike with one to four whorls of flowers, submersed or emersed, unbranched, 1.5 - 10 mm long, on a terminal or axillary stalk. Stalks one to three per plant, thread-like to cylindrical, 0.5 - 6 cm long.

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

Fruit: an achene, stalkless, green to brown, 1.5 - 2 mm long, 1 - 1.5 mm wide, reverse egg-shaped, concave, not keeled, with an upright, 0.1 - 0.6 mm long beak. When in fruit, the inflorescence is interrupted.

Similar species: The interrupted inflorescence during fruiting and the narrowly linear, one- to three-veined leaves help distinguish this species.

Flowering: July to mid-September

Habitat and ecology: This species is found nearly all over the world. Found in lakes, ponds, streams, and ditches, especially in calcareous waters.

Occurence in the Chicago region: native

Notes: Plants in the genus Potamogeton are very important to wildlife, offering habitat and food for many aquatic animals.

Etymology: Potamogeton comes from the Greek words potamos, meaning river, and geiton, meaning neighbor, referring to the habitat of these plants. Pusillus means insignificant, weak, or very small.

Author: The Morton Arboretum

Our specimens are from northern lakes.