Botanical Facts
Flowering and Dormancy
The Smallest Fruit
Botanical Description
Taxonomy / Key
Duckweed Evolution
Duckweed Roots
Biochemistry & Physiology
Botanical Drawings
Geographic Distribution
Rapid Growth Duckweed Habitat

Duckweed in full bloom
Flowering Lemna gibbaClose-up of flowering Lemna gibba.

Lemna flowers consist of two stamens (pollen bearing organs) and a single style (pollen receptive organ). 

This plant has two leaves and a single root extending at the bottom of the picture.  The flower is at the top of the photograph.  It consists of two stamens (pollen bearing organs) and a single style (pollen receptive organ).  At its top, each stamen bears an anther where the pollen develops.   The stigma, which will receive the pollen in fertilization, is the cup-shaped body atop the stigma.  The ovary is at the base of the style.

 Read more about flowering and dormancy in duckweeds and the world's smallest fruit.

Photo from Wayne Armstrong's Web site, Key to the Lemnaceae Of North America.

Although duckweeds can set seed and produce fruit like other flowering plants, they mostly reproduce vegetatively.  The leaves of duckweeds commonly are called fronds, but are not considered fronds by strict botanical definition.  Unlike the ordinary leaves of most plants, each duckweed frond contains buds from which more fronds may grow.  These buds are hidden from view 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. See and read more on duckweed anatomy.

Taxonomy / Key. 
There are five genera (genuses) in the the Lemnaceae (Duckweed Family).  The simplified key below adapted from Wayne P. Armstrong's Key to the Lemnaceae of Western North America.  The links on the right side of the table describe each genus in pictures.  Note: pages with pictures may load slowly.
Key Characteristic
Plant body (frond) has one or more roots. 
(click on link for drawings and photos)
    One root:  Lemna
    Two or more roots: Spirodela and Landoltia
Plant body has no roots
    Flattened plant body: Wolffiella
    Oval-shaped plant body, less than 1 mm: Wolffia


Three duckweed genera together:   Spirodela (largest), Lemna (mid-sized) and Wolffia (smallest), scale in millimeters. 

Photo by Gerald Carr, University of Hawaii.

A Formal Botanical Description in industrial-strength botanical language is available by L. Watson and M.J. Dallwitz. [ Interactive Key ]

"Habit and leaf form. Much reduced, aquatic herbs. Plants of very peculiar vegetative form; thalloid (thallus small to minute, globular, flat or linear, with one (Wolffioideae) or two (Lemnoïdeae) budding pouches, raphides present with mucilage cells in Lemnoïdeae only, xylem without vesses, phloem transfer cells lacking at least in Lemna). Leaves absent. Plants with roots (usually, in Lemnoïdeae), or rootless (Wolffioïdeae). Annual. Hydrophytic; free floating. ."

Botanical Drawings

From L. Watson and M.J. Dallwitz:  • Technical details: Lemna. • Technical details: Wolffia (including Grantia, Telmatophace). • Lemna gibba: Eng. Bot. 1396 (1869). • Lemna minor: Eng. Bot. 1395 (1869). • Lemna polyrrhiza: Eng. Bot. 1397 (1869). • Lemna trisulca: Eng. Bot. 1394 (1869). • Wolffia arrhiza: as Lemna, Eng. Bot. 1398 (1869).
Note that the species labeled Grantia microscopica is likely a synonym for Wolffia microscopica.)

From virtual biological library, courtesy of Kurt Stüber, Max-Planck-Institut für Züchtungsforschung, Cologne, Germany:  • Flora von Deutschland Österreich und der Schweiz by Prof. Dr. Otto Wilhelm Thomé, 1885,  •  Handbuch der Systematischen Botanik (1924) 

Recent Taxonomic Research  (not available on-line).

Les, D.H., Landolt, E., Crawford, D.J. (1997) Systematics of the Lemnaceae (Duckweeds): inferences from micromolecular and morphological data. Plant Systematics and Evolution  204: 161-177.

Les, D. H. & D. J. Crawford. (1999) "Landoltia (Lemnaceae), a new genus of duckweeds." Novon 9: 530-533.

Les, Donald H., Crawford, Daniel J., Landolt, Elias, Gabel, John D., Kimball, Rebecca T. (2002) "Phylogeny and Systematics of Lemnaceae, the Duckweed Family" Systematic Botany 27: 221-240.

Duckweed Evolution:  Where did the duckweeds come from?  How are the different species related?

Learn more firsthand.  If you are interested in duckweeds, try some experiments yourself.  They are easily grown in small containers outside or in the laboratory.

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Last revised:  May 23, 2014