Species commonly cultivated
Spirodela polyrhiza (L.) Schleid. (cosmopolitan)
S. punctata (G. Mey.) C.H. Thomps. (Australia, Asia, America, Africa)
information not available
Spirodela polyrhiza is a serious weed in rice fields in Asia, South America, and Europe. It has shown resistance to diquat in Florida.
free floating, minute, thallus-like plant
Minute, free-floating on water surface. Reduced plant body, undifferentiated into stem and leaf. Frond broadly ovate to orbicular, green above, red below, venation palmate; margin entire. Roots unbranched, 2-21 arising from center of fronds. Daughter fronds borne in two ventral budding pouches, attached to mother frond by short stipe. Vegetative turions produced near base of roots. Inflorescence minute, rarely occurring, unisexual, of 1 female and 2 male flowers enclosed in a membranous spathe, produced from budding pouch. Dispersal by frond budding, seeds, and resting turions.
still waters of lakes, rivers, and swamps
Spirodela contains three species worldwide, but only S. polyrhiza and S. punctata are commonly cultivated for aquaria. This genus has the largest sized plants in the family and is the only genus with multiple roots arising from each frond. One species of this genus (S. punctata) has been moved to the genus Landoltia Les & D.J. Crawford based on molecular data. Spirodela polyrhiza is larger and rounder, and has more roots (5-21) per frond than S. punctata (2-12).
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 one.......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