Roots 7--21, to 3 cm, 1 or 2 perforating scale. Fronds obovate to circular, flat or rarely gibbous, 2--10 mm, 1--1.5 times as long as wide, apex rounded or pointed, upper surface sometimes with red spot in center; veins 7--16(--21); turions sometimes present, rootless, brownish olive, circular-reniform, 1--2 mm diam. Flowers: ovaries 1--2-ovulate. Fruits 1--1.5 mm, laterally winged to apex. Seeds with 12--20 distinct ribs. 2n = 30 , 38, 40, 50, 80.

Flowering (very rare) early summer--early fall. Eutrophic, quiet waters, in temperate to tropical regions; 0--2500 m; Alta., B.C., Man., N.B., N.S., Ont., P.E.I., Que., Sask.; 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.; nearly worldwide.

Plant: small aquatic plant

Leaves: FRONDS obovate to circular, rounded or pointed at the apex, 1.5-10 mm long, 1-1.5 times as long as wide, flat or rarely gibbous, sometimes with a red spot in the center of the upper surface; nerves 7-16(-21)

Flowers: very rare, 1-2-ovulate, the stamens 2, 4-locular

Fruit: 1.0-1.5 mm long, laterally winged to the top; SEEDS 1-3, with 12-20 distinct ribs

Misc: Rather eutrophic, quiet waters; below 2450 m (8000 ft); Jun-Sep

Notes: roots 7-21, up to 3 cm long; turions sometimes present, small, circular to reniform, brownish to olive, rootless

REFERENCES: Landolt, Elias. 1992. Lemnaceae. Ariz.-Nev. Acad. Sci. 26(1)2.

Aquatic herb

Flowers: occurring very rarely, lacking sepals and petals, with two stamens, surrounded by a small membranous scale.

Fruit: bladder-like (utricle), thin-walled, 1 - 1.5 mm long, laterally winged, seeds having twelve to twenty ribs.

Roots: two to 21 per frond, to 3 cm long, with a small membranous scale surrounding attachment point.

Plant body: not differentiated into stem and leaves, green and often with a red dot above, purplish beneath, 2 - 10 mm long, one to one and a half times as long as wide, flattened, inversely egg-shaped to broadly egg-shaped with a rounded or pointed tip, five- to sixteen-veined, with air spaces in plant body tissue. Two triangular reproductive pouches produce daughter plants and flowers.

Winter buds: rootless, brownish to olive, circular to kidney-shaped.

Similar species: Lemna species differ from Spirodela polyrrhiza by having solitary roots and plant bodies with five or fewer distinct veins.

Flowering: early summer to early fall

Habitat and ecology: Frequent in lakes, ponds, and other standing or slow-moving water.

Occurence in the Chicago region: native

Etymology: Spirodela comes from the Greek words, speira, meaning spiral, and delos, meaning evident, referring to the spiral vessels of this plant that are clearly visible. Polyrrhiza means many-rooted.

Author: The Morton Arboretum

Locally abundant throughout the state in lakes, ponds, swamps, ditches, and sluggish streams. These plants are preyed upon by insects.

Thallus broadly oval to obovate, anthocyanic beneath, (3-)5-8(-10) mm, ±evidently 5-15-nerved, forming turions especially in the fall; roots mostly 5-12; spathe open only at the top; seeds 1 or 2, smooth or minutely reticulate; 2n=30, 40, 50. Quiet water; nearly cosmopolitan, and throughout our range.

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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