Potamogeton friesii Rupr.
Family: Potamogetonaceae
Flat-Stalk Pondweed
Potamogeton friesii image
Rhizomes absent. Cauline stems compressed, without spots, 10--135 cm; glands green, greenish brown, or gold, to 0.7 mm diam. Turions terminal or lateral, common, 1.5--5 cm ´ 1.5--4 mm, soft; leaves ± 4-ranked; outer leaves 2--3 per side, base corrugate, apex apiculate to acute; inner leaves reduced, arranged into fan-shaped structure and oriented at 90° angles to outer leaves. Leaves submersed, ± spirally arranged, delicate to rigid, sessile; stipules not persistent, inconspicuous, convolute, free from blade, white, not ligulate, 0.55--2.1 cm, fibrous, coarse, shredding at tip, apex obtuse; blade light green, rarely olive-green to .somewhat reddish, linear, not arcuate, 2.3--6.5 cm ´ 1.2--3.2 mm, base slightly tapering, without basal lobes, not clasping, margins entire, not crispate, apex not hoodlike, acute to apiculate, lacunae absent or 1 narrow row each side of midrib; veins 5--7(--9). Inflorescences unbranched, emersed; peduncles not dimorphic, terminal or axillary, erect or rarely recurved, slightly clavate, 1.2--4.1(--7) cm; spike not dimorphic, cylindric, 7--16 mm. Fruits sessile, olive-green to brown, obovoid, turgid, not abaxially or laterally keeled, 1.8--2.5 ´ 1.2--2 mm; beak erect, 0.3--0.7 mm; sides without basal tubercles; embryo with 1 full spiral. 2n = 26. Flowering and fruiting summer--fall. Calcareous to brackish waters of lakes and slow-flowing streams; 0--3100 m; Alta., B.C., Man., N.B., Nfld. and Labr. (Nfld.), N.W.T., N.S., Ont., P.E.I., Que., Sask., Yukon; Alaska, Colo., Conn., Idaho, Ill., Ind., Iowa, Maine, Mass., Mich., Minn., Mont., Nebr., N.H., N.Y., N.Dak., Ohio, Pa., R.I., S.Dak., Utah, Vt., Wash., Wis., Wyo.; Eurasia. Potamogeton friesii is a fairly common linear-leaved species, especially of calcareous waters of lakes and streams of the upper Midwest. Whenever turions are present, the species is easily identified, as it is the only one with the outer leaves of the turions having corrugate bases and the inner leaves turned at right angles to the outer leaves. Two hybrids, Potamogeton friesii ´ P. pusillus (= P. ´ pusilliformis Fischer [P. ´ intermedius Fischer]) and P. friesii ´ P. obtusifolius (= P. ´ semifructus A. Bennett ex Ascherson & Graebner), have been described.

Perennial submersed aquatic herb 10 cm - 1 m tall Stem: sparsely branched below, slightly compressed, to 1 mm wide, jointed, often with paired nodal glands. Turions (small, over-wintering shoots) 1.5 - 5 cm long, with corrugate-based outer leaves and fan-shaped inner leaves set at right angles to the outer ones. Leaves: submersed, more or less arranged spirally, stalkless, translucent, light green, 2 - 7 cm long, 1 - 3 mm wide, linear with a slightly tapering base and pointed tip (with a short, tiny point), typically five- to seven-veined. Stipules axillary, free from leaf blade, white, rolled up, 0.5 - 2 cm long, becoming fibrous with age. Inflorescence: an upright, slender, cylindrical spike with two to five whorls of flowers, emersed, unbranched, 0.7 - 1.6 cm long, on a terminal or axillary stalk. Stalk flattened, slightly club-shaped, 1 - 5 cm long. Flowers: greenish, tiny. Stamens four. Anthers two-chambered, with four edge-to-edge sepal-like outgrowths. Fruit: an achene, stalkless, olive green to brown, 2 - 2.5 mm long, 1 - 2 mm wide, reverse egg-shaped with rounded sides, plump, not keeled, with an upright, 0.3 - 0.7 mm long beak.

Similar species: This species is easily identified by its turions (small, over-wintering shoots), which have corrugate-based outer leaves and fan-shaped inner leaves set at right angles to the outer ones.

Flowering: July to early August

Habitat and ecology: Occasional in lakes with clear water.

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. Friesii is named after Elias Magnus Fries (1794-1878), a Swedish botanist.

Author: The Morton Arboretum

Stem to 1 m or more, sparingly branched below, often more freely so above, slightly compressed, to 1 mm wide, commonly with paired glands at the nodes; rhizome scarcely developed; lvs all submersed, linear, 3-7 cm נ1.5-3 mm, minutely cuspidate at the obtuse or rounded tip, (3)5-7(9)-veined, the lateral veins very delicate, the midvein flanked by a row of lacunar cells on each side extending two-thirds its length, or these wanting; stipular sheaths axillary, free, white, 0.5-2 cm, closed at base when young, becoming fibrous in age; winter-buds commonly produced, 1.5- 5 cm, the inner lvs reduced and arranged into a fan-shaped structure, set at right angles to the outer lvs; peduncles 1.5-5 cm, flattened and clavate; spike slender, 8-18 mm, with 2-5 remote whorls of fls; frs ovoid to obovoid, 2-3 mm, with rounded sides, not or scarcely keeled; 2n=26. Chiefly in calcareous waters; Que. and Nf. to Mack. and Alas., s. to N.J., Pa., and Ind., n. Io., Nebr., and Utah.

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

©The New York Botanical Garden. All rights reserved. Used by permission.
From Flora of Indiana (1940) by Charles C. Deam
In a few of our northern lakes.