Roots to 2.5 cm (sometimes not developed), tip pointed; sheath not winged. Green stalks 2--20 mm. Fronds submersed (except when flowering or fruiting), 3--50, coherent and very often forming branched chains, narrowly ovate, flat, thin, 3--15 mm (excluding stalk), 2--3.5 times as long as wide, base suddenly narrowed into green stalk, margins denticulate distally; veins (1 or) 3, lateral veins only in proximal part of frond; papillae absent; anthocyanin often present; air spaces shorter than 0.3 mm; turions absent. Flowers: ovaries 1-ovulate, utricular scale with narrow opening at apex. Fruits 0.6--0.9 mm, laterally winged toward apex. Seeds with 12--18 distinct ribs, staying within fruit wall after ripening. 2n = 40, 42, 44, 60, 63, 80.
Flowering (rare) late spring--summer. Mesotrophic, quiet waters rich in calcium, in cool-temperate regions; 0--3000 m; Alta., B.C., Man., N.B., N.W.T., N.S., Nunavut, Ont., P.E.I., Que., Sask., Yukon; Alaska, Ariz., Ark., Calif., Colo., Conn., Idaho, Ill., Ind., Iowa, Kans., Maine, Md., Mass., Mich., Minn., Mo., Mont., Nebr., Nev., N.H., N.J., N.Mex., N.Y., N.Dak., Ohio, Oreg., Pa., R.I., S.Dak., Tenn., Utah, Vt., Va., Wash., W.Va., Wis., Wyo.; nearly worldwide, except arctic and antarctic regions and South America; in warm regions only in mountains.
The report of Lemna trisulca in Florida is dubious because the climate is too warm. The species may be temporarily introduced there by birds.
Plant: small aquatic plant Leaves: FRONDS submerged, 3-50 cohering and very often forming branched chains, narrowly ovate, 3-15 mm long (without stalk), 2-3.5 times as long as wide, flat and thin, narrowed at the base into a 2-20 mm long green stalk; margins distally denticulate; nerves (1-)3, the laterals only in the lower part of the frond; papillae absent; anthocyanin often present; air spaces smaller than 0.3 mm Flowers: rare (the flowering fronds floating on the water's surface), 1-ovulate, the small utricular scale with a narrow opening at the top Fruit: 0.6-0.9 mm long, laterally winged towards the top SEEDS: with 12 to 18 distinct ribs Misc: Mesotrophic, quiet waters rich in calcium; 2100-2700 m (7000-9000 ft); May-Aug Notes: root up to 2.5 cm long (sometimes not developed), the sheath unwinged, the tip pointed; turions absent REFERENCES: Landolt, Elias. 1992. Lemnaceae. Ariz.-Nev. Acad. Sci. 26(1)2.
Aquatic herb Flowers: occurring rarely, lacking sepals and petals, with two stamens, surrounded by a membraneous scale with a narrow opening at the tip. Fruit: bladder-like (utricle), thin-walled, 0.6 - 0.9 mm long, winged laterally toward tip, seeds having twelve to eighteen distinct ribs and remaining in fruit wall after ripening. Roots: to 2.5 cm long with a pointed tip, sometimes absent. Plant body: not differentiated into stem and leaves, submersed (except when flowering and fruiting), often forming a branched mass of three to 50, connected by green stalk-like structures (stipes) 2 - 20 mm long, green, sometimes with some purple, 3 - 15 mm long, two to three and a half times as long as wide, flattened, oblong lance-shaped to elliptic or narrow egg-shaped with base suddenly narrowing into stipe and margins finely toothed near tip, three-veined, projections absent. Air spaces inside the plant body are shorter than 0.3 mm.
Similar species: Lemna trisulca is easy to distinguish from other species of Lemna by having a submersed branched mass of plant bodies connected by distinctive green stalk-like structures (stipes).
Flowering: late spring to summer
Habitat and ecology: Frequent in quiet waters, but not as common as Lemna minor.
Occurence in the Chicago region: native
Etymology: Lemna is the Greek name for a water weed. Trisulca means three-furrowed.
Thallus thin, oval or oblong, denticulate or erose toward the tip, obscurely 3-nerved, tapering to a 4-16 mm stipe that remains attached to the parent plant, forming tangled colonies, mostly floating just beneath the water-surface, emersed in fl and fr; spathe open; seed solitary; 2n=20, 40, 60, 80. Widespread in both the Old and New Worlds, 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.