Common names: duck weed, water meal

Family: Lemnaceae

Could be confused with: Wolffiella, Lemna.

Native distribution: Almost Cosmopolitan.

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)

Adventive distribution: Wolffia globosa is introduced into North America.

Weed status: Often a minor weed in eutrophic waters and rice fields.

Habit: Free-floating, very minute, thallus-like plant.

Brief description: 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.

Note that Wolffia fronds may aggregate or daughter frond(s) may remain attached to the parent plant, and as a result may appear to be a single lobed frond but are not.

Natural habitat: Still waters of lakes, rivers and swamps.

Additional comments: 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:

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