Lemna minor is introduced into Japan, Australia, and New Zealand, while L. minuta Kunth ex. Humb. is introduced in Asia and Europe.
a weed of rice fields
free-floating, minute, thallus-like plant
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.
still waters of lakes, rivers, and swamps
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:
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.
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