Lemna minor

Lesser Duckweed

Lesser Duckweed
Photo Courtesy USDA Plants Database

Flora, fauna, earth, and sky...
The natural history of the northwoods

Name:

• Lemna, from the Greek, lemna, "water-plant, star-grass, Callitriche verna"
• minor, from the Latin, "lesser"
• Common Name, from its size relative to that of the other common North American duckweed, Greater Duckweed (Spirodela polyrhiza)
• Other common names include: Common Duckweed, Duck's Meat, Lenticule mineure (Qué), Liden Andemad (Dan), Väike lemmel, Konnaläätsed, Vesiläätsed, Seauba, Vesivirn, Päevaseep, Tiigieile (Est), Pikkulimaska (Fin), Mac gun Athair (Gaelic), Kleine Wasserlinse (Ger), Klein Kroos (NL), Andmat (Nor), Zaburinka Menšia (Slovak), Andmat, Vanlig Andmat (Swe)

Taxonomy:

• Kingdom Plantae, the Plants
  • Division Magnoliophyta, the Angiosperms (flowering plants)
    • Class Liliopsida, the Monocotyledons
    • Subclass Arecidae, the Arum
      • Order Arales, the Arum
        • Family Lemnaceae, the Duckweeds As a result of their adaptation to aquatic habitats, they are among the smallest and simplest of the flowering plants, floating monocotyledons, only 1-15mm in size.
          • Genus Lemna, 13 species worldwide.
• Taxonomic Serial Number: 42590
• Also known as Lemna cyclostasa, Lemna minima

Description:

• A ¼, ½, ¾, º, é
• A diminutive floating aquatic perennial, often forming a solid cover on the surface.
• Leaves and Stems merged in common structure typically called a frond or thallus, though neither term is correct by strict botanical definition. The frond itself consists of one to several layers of conspicuous air spaces and one to several veins.
• Frond flattened, suborbicular to elliptic-obovate in outline; generally symetrical, with smooth upper surface. The smallest North Country Duckweed, the fronds rarely exceed 1/8" in diameter. They have three veins. Two budding pouches are locaed on either side of the basal end. Fronds solitary or in connected clonal clusters of 2 to 5.
• Root one
• Flower of 2 stamens and a single pistel in a membranous saclike spathe, hidden away inside the budding pouches. Flowers uncommon.
• Because Duckweed is largely made up of metabolically active cells with very little structural fiber, the tissue contains twice the protein, fat, nitrogen, and phosphorus of other vascular plants. Each frond absorbs nutrients through the whole plant and not through a central root system, directly assimilating organic molecules such as simple carbohydrates and various amino acids. With the entire body of the duckweed composed of non-structural, metabolically active tissue, most photosynthesis is devoted to the production of protein and nucleic acids, making them very high in nutrional value.
• Roots to 15 cm, tip mostly rounded; sheath not winged. Stipes white, small, often decaying. Fronds floating, 1 or 2--5 or more, coherent in groups, ovate, scarcely gibbous, flat, 1--8 mm, 1.3--2 times as long as wide, margins entire; veins 3(--5) (if more than 3, outer ones branching from inner ones), greatest distance between lateral veins near or proximal to middle; papillae not always distinct (one near apex usually larger); lower surface very seldom slightly reddish (much less than on upper), coloring beginning from attachment point of root, upper surface occasionally diffusely reddish; air spaces 0.3 mm or shorter; distinct turions absent. Flowers: ovaries 1-ovulate, utricular scale with narrow opening at apex. Fruits 0.8--1 mm, laterally winged toward apex. Seeds with 8--15 distinct ribs, staying within fruit wall after ripening.

Identification:

• Identifiable as a Duckweed by its diminutive size and free-floating habit.
• Distinguished from Greater Duckweed (Spirodela polyrhiza) by its single root and much smaller size.
• Distinguished from Ivy Leaf Duckweed (Lemna trisulca) by its small, round fronds.

Distribution:

• Widespread throughout temperate regions of the northern and southern hemispheres, including North America, Eurasia, Australia, and New Zealand.

Habitat:

• Freshwater ponds, marshes, lakes, and quiet streams.
• Spreads rapidly across quiet bodies of water rich in nutrients, growing best in water with high levels of nitrogen and phosphate. Iron is often limiting. Can tolerate a wide pH range, but survives best between 4.5 and 7.5.
• A cover of duckweed fronds shades the water below and reduces the growth of algae. Floating duckweed plants are relatively easy to remove by skimming or are eaten by herbivorous fish. These traits make duckweeds useful in nutrient removal and bioremediation schemes.
• Grows in full sunlight as well as dense shade.
• More cold tolerant than other aquatic vascular plants, and can sustain temperatures as low as 7º Celcius for normal, practical growth. Under freezing conditions, will lay dormant on the pond bottom until warmer conditions return. A full, thick mat of duckweed may have a temperature of about 10º above ambient air conditions due to radiation
• Wind and wave action can impede duckweed growth and stabilization by disrupting their ability to attach themselves to each other and form their characteristic homogenous colonial populations. Optimal conditions for growth are quiet streams and ponds
• Flowering (rare) late spring--early fall. Mesotrophic to --eutrophic, quiet waters, in suboceanic, cool-temperate regions with relatively mild winters; 0--2000 m; St. Pierre and Miquelon; B.C., Ont., Que., Sask.; Ala., Ariz., Ark., Calif., Conn., Del., D.C., Fla., Idaho, Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Mo., Mont., Nebr., N.H., N.J., N.Mex., N.Y., N.C., N.Dak., Ohio, Okla., Oreg., Pa., R.I., S.Dak., Tenn., Utah, Vt., Va., Wash., W.Va., Wis.; w Eurasia; Africa; Atlantic Islands; Australia (introduced), New Zealand (introduced).

Associates:

• Natural populations of duckweeds are usually mixtures of several species.
• Trees: Tammarack (Larix laricina), Black Spruce (Picea mariana)
• Shrubs: Bog Birch (Betula pumila), Leatherleaf (Chamaedaphne calyculata), Sweet Gale (Myrica gale)
• Herbs: Blue Flag Iris (Iris versicolor), Cattails (Typha spp)
• Ground Covers: Sphagnum Mosses (Sphagnum spp.)
• Mammals: Moose (Alces alces)
• Birds: Great Blue Heron (Ardea herodias)

History:

• ". . . The green mantle of the stagnant pool" (King Lear, Act III, Scene 4 - A reference to Lemna minor?)

Uses:

• Very important in the ecosystem as an essential link in the food chain.
• Useful as a water crop as they can acclimatize themselves to almost all growing conditions, with some thriving in manure-rich or eutrophic waters. They reproduce quickly, extending over large surface areas, and are easily harvested. Their high fat and protein content makes them a source of food for animals and poultry.
• Duckweeds have potential in wastewater treatment, absorbing excess nutrients from surface waters, including phosphorus and ammonias, reducing suspended solids, and reducing biochemical oxygen demand.

Reproduction:

• Reproduces by seed and vegetatively, thought during the growing season, nearly all plants arise by vegetative reproduction.
• Unlike the ordinary leaves of most plants, each duckweed frond contains buds from which more fronds may grow. These buds are hidden in pouches along the center axis of older fronds. As they grow, new fronds emerge through slits in the side of their parent fronds. Until they mature, daughter fronds may remain attached to the parent frond. Rapidly growing plants often have three or four attached fronds.
• In fall, budding pouches produce smaller, rootless, dark green or brownish daughter plants called turions. These dense, dormant, starchfilled structures sink in the fall and rise in the spring due to changes in starch composition and gas spaces. Other aquatic plants form turions which are distinctive terminal buds, but Lesser Duckweed turions are very similar to ordinary fronds, just darker green and a bit smaller
• Although Duckweed can set seed and produce fruit like other flowering plants, flowers and seed are uncommon.
• Plants may overwinter as turions, or as seeds, sinking and resting at the bottom of the pond until they germinate.
• Duckweed reproduce at twice the rate of other vascular plants. Under ideal conditions, the frond area can double in a few days.

Propagation:

• By benign neglect

Cultivation:

• Hardy to USDA Zone 3 (average minimum annual temperature -40ºF)
• Easily grown in garden ponds, where it removes excess nutrients from the water while providing surface shade, both of which act to inhibit algae growth.
• Like most water plants, does best in full sun.
• Goldfish, and other carp, are particularly fond of duckweed. Keep a "starter batch" in a separate, fish free container or pond, if the fish are too voracious.
• Can be invasive in garden ponds without goldfish, but can be controlled rather easily by surface skimming with a hand skimmer from a swimming pool supplier. Just throw it in the compost - it's rich in nutrients.

Links:

• Den virtuella floran, from the Naturhistoriska riksmuseet, Stockholm
• The Charms of Duckweed
• Key to the Lemnaceae of Western North America, index to genera from Wayne Armstrong, Oregon State University

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