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Aquatic and Wetland Vascular Plants of the Northern Great Plains

Lemnaceae - The Duckweed Family


Small or minute thalloid plants with bodies not differentiated into stems and leaves, free-floating on or beneath the water surface.* Thalli reproducing vegetatively by budding from one or two pouches on the sides, the parent thallus and budded thalli often cohering in groups of 2-several, each thalloid segment commonly referred to as a "frond." Roots, if present, 1-several hanging down from near the center on the underside of each frond, short, unbranched, fine. Flowers rarely present, imperfect, contained in tiny reproductive pouches or pits at the edge (Lemna, Spirodela) or on the upper surface (Wolffia) of the frond, subtended by a spathe within the reproductive pouch; perianth none, staminate flowers 1 or 2, each comprised of a single anther on a short filament; pistillate flower 1, contained in the same pouch as the staminate flower(s), consisting of a single flask-shaped ovary. Fruit autricle containing 1-few seeds.

*The aquatic liverworts, Riccia and Ricciocarpus are occasionally encountered in fresh waters of this region. These nonvascular plants resemble the duckweeds in size and growth habit and, in fact, are sometimes collected with duckweeds. Riccia fluitans appears as a very narrow (ca. 1 mm wide), bifurcating, ribbonlike thallus, free-floating and lacking rhizoids. Ricciocarpus natans has a broadly lobed rosette form with numerous rhizoids on the underside. When stranded on mud, the thallus is nearly radially symmetric with the rhizoids anchored in the substrate. The free-floating form is more bilaterally symmetric with conspicuous reddish rhizoids trailing beneath the thallus.

References:

Clark, H. L. and J. W. Thieret.  1968.  The duckweeds of Minnesota.  
     Michigan Bot. 7:67-75

Daubs, E. H.  1965.  A monograph of Lemnaceae.  Illinois Biol. Monogr.  
     34:1-118. 

Hartog, C. den and F. van der Plas.  1970.  A synopsis of the Lemnaceae.  	
     Blumea 18:355-368. 

Landolt, E.  1980.  Biosystematic investigation of the family of duckweeds 
     (Lemnaceae), vol. 1.  Veroff. Geobot. Inst. ETH, Stiftung Rubel, 
     Zurich, 70:1-247.

Lead Characteristic Go To
1 Fronds thickened, less than 1.5 mm long, lacking roots. Genus Wolffia
1 Fronds flat, mostly longer than 1.5 mm long, with 1-several roots trailing from the lower side. Lead 2
2 Each frond with 3 or more roots; underside of the frond solid purple. Genus Spirodela
2 Each frond with a single root; underside of the frond green or purple-tinged or mottled. Genus Lemna


60. Lemnaceae, the Duckweed Family
1. Lemna L. -- Duckweed
1. Lemna aequinoctialis Welw.
2. Lemna gibba L.
3. Lemna minor L.
4. Lemna minuscula Herter
5. Lemna obscura (Austin) Daubs
6. Lemna perpusilla Torr.
7. Lemna trisulca L. -- Star duckweed
8. Lemna turionifera Landolt
2. Spirodela Schleid. -- Duck-meat
1. Spirodela polyrrhiza (L.) Schleid.
3. Wolffia Horkel -- Water-meal
1. Wolffia borealis (Engelm.) Landolt
2. Wolffia columbiana Karst.


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