Wolffia Horkel ex Schleid.
duck weed, water meal
Species commonly cultivated
Wolffia angusta Landolt (Asia to Australia)
W. arrhiza (L.) Horkel ex Wimm. (Europe, Africa, South America)
W. globosa (Roxb.) Hartog & Plas (Asia, North and South America)
W. welwitschii (Hegelm.) Monod (Africa, Central and South America)
Wolffia globosa is introduced into North America.
often a minor weed in eutrophic waters and rice fields
free-floating, very minute, thallus-like plant
Minute (rarely exceeding 1 mm), free-floating on or just below water surface. Reduced plant body, undifferentiated into stem and leaf. Roots absent. Fronds broadly ovate, spherical to oblong, venation absent; margin entire. Daughter fronds borne in a funnel-shaped basal budding pouch with a circular opening. Inflorescence rarely occurring, minute, of 1 female and 1 male flower. Flowers produced in budding pouch in middle of frond. Membranous spathe lacking. Dispersal by frond budding and seeds.
still waters of lakes, rivers, and swamps
Wolffia globosa is the world's smallest flowering plant (size: 0.5 mm x 0.3 mm). Wolffia is a cosmopolitan genus containing 10 species. Three species are commonly cultivated, although usually inadvertently, in aquaria and ponds.
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