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Species: Wolffia spp., watermeal
Wolffiella gladiata Hegelm., mud midget
Family: Lemnaceae

Watermeal and mud-midget are the smallest flowering plants in the world. Watermeal plants are tiny, globular plants without roots. They sometimes occur in colonies that form bright green mats on sheltered waters. There are several different watermeal species in North America, all of which closely resemble one another. The different species can only be identified with magnification.  Mud-midget plants are elongate in shape, and look like small bits of grass arranged in star-shaped clusters floating just beneath the water surface.

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Leaf: No true leaves. The leaf-like body is called a thallus. Water-meal: roundish, thick, thallus up to 1.3 mm in diameter. Mud-midget: thin, sickle-shaped thallus up to 9 mm long and 1.5 mm wide, plants tend to form star-shaped clusters.

Stem: None.

Flower: Tiny, rarely seen. Arises from a cavity on the upper surface of the thallus.

Fruit: Balloon-like fruit (utricle) contains a tiny (0.5 mm) smooth seed. 

Root: None.

Propagation: Seeds. Forms winter buds on the lake bottom. New plants can bud from a pocket on the basal end of the parent plant and eventually the plants break apart. The plants are distributed by wind, and on the bodies of birds, muskrats, and other animals.

Importance of plant: Provides food for fish and waterfowl, and habitat for aquatic invertebrates. Because of its high nutritive value, these plants have been used for cattle and pig feed in Africa, India, and southeast Asia. One species of watermeal is cultivated and eaten as a vegetable in Burma, Laos, and Thailand.

Distribution: The different species are found throughout much of the temperate and subtropical regions of the world. Mud midget may have been introduced to Washington from the southern U.S., but may not be winter hardy.

Habitat: Marshes, ponds, shallow edges of lakes, slowly moving streams, and ditches. Often found on wet soil when water levels drop.

May be confused with:  Duckweeds (Lemna spp.) which are larger and have at least 1 root. Giant duckweed (Spirodela polyrrhiza) is larger, reddish-purple on the undersides, and has a cluster of 7 to 21 roots from each leaf-like body. Mexican water fern (Azolla mexicana) is also larger and is greenish red with a nubby texture. Watermeal also may resemble an algae bloom for a distance, but its mealy texture is distinctive.

Photographs: Wolffia sp closeup, Wolffiella gladiata closeup

Line Drawings: Wolffia sp.


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