Lemna

Scientific name

Lemna L.

Common names

duckweed

Family

Lemnaceae

Could be confused with

Spirodela, Wolffia, Wolffiella

Native distribution

cosmopolitan

Species commonly cultivated

Lemna aequinoctialis Welw. (Asia, Australia)

L. gibba L. (America, Asia, Europe, Africa)

L. minor L. (cosmopolitan)

L. trisulca L. (cosmopolitan, except South America)

Adventive distribution

Lemna minor is introduced into Japan, Australia, and New Zealand, while L. minuta Kunth ex. Humb. is introduced in Asia and Europe.

Weed status

a weed of rice fields

Habit

free-floating, minute, thallus-like plant

Brief description

Minute, free-floating on or (rarely) below water surface. Reduced plant body, undifferentiated into stem and leaf. Frond broadly ovate to oblong, not lobed or divided (except L. trisulca), sometimes with a narrow petiole-like base (e.g. L. trisulca), venation palmate; margin entire or with slight serrations on apical margin; daughter fronds borne in two ventral budding pouches. Roots solitary, unbranched, arising from center of each frond or (rarely) absent. Inflorescence rare, minute, of 1 female and 2 male flowers enclosed in a membranous spathe, borne in budding pouch. Dispersal by frond budding and seeds.

Natural habitat

still waters of lakes, rivers, and swamps

Additional comments

A cosmopolitan genus containing 13 species. Three species are commonly cultivated, although usually inadvertently, in aquaria and ponds. The monotypic genus Landoltia is morphologically not very different from Lemna, and may not warrant separation of Landoltia punctata (G.F.W. Meyer) Les & Crawford into its own genus. Molecular data (Les and Crawford 1999) suggest that Landoltia is indeed justified. A short dichotomous key to Lemnaceae is presented below.

An excellent resource for all Lemnaceae can be found at this website:

'Wayne Armstrong's treatment of the Lemnaceae'

A dichotomous key to the genera of Lemnaceae (source: Armstrong 2003):

1a. Plant body with 1 - several roots.

2a. Root 1.......Lemna

2b. Roots 2 - 12.

3a. Roots 7 - 12 (or more); plant 10 mm long.......Spirodela

3b. Roots 2 - 3 (up to 5); plant 3 - 6 mm long.......Landoltia

1b. Plant body without roots.

4a. Plant body flattened; 3 - 10 mm long......Wolffiella

4b. Plant body globose-ovoid; 0.6 - 1.2 mm long.......Wolffia