Duckweed, also known as
water lentil, is the smallest flowering plant in the world. The plant consists of a short stem floating vertically in the water, roots in
Spirodela and
Lemna, and occasionally a
flower consisting of two stamens and a pistil (some call it an
inflorescence consisting of three unisexual flowers). The
fruit is a utricle, a sac containing air and a seed designed to float; that of
Wolffia is the smallest in the world, 0.3 mm long. Reproduction is usually by budding (as in
yeast; in flowering plants, such structures are usually called runners).
The family contains four to six genera (depending on the taxonomist) and is believed to be descended from Araceae.