1911 Encyclopædia Britannica/Duckweed
DUCKWEED, the common botanical name for species of Lemna which form a green coating on fresh-water ponds and ditches. The plants are of extremely simple structure and are the smallest and least differentiated of flowering plants. They consist of a so-called “frond”—a flattened green more or less oval structure which emits branches similar to itself from lateral pockets at or near the base. From the under surface a root with a well-developed sheath grows downwards into the water. The flowers, which are rarely found in Britain, are developed in one of the lateral pockets. The inflorescence is a very simple one, consisting of one or two male flowers each comprising a single stamen, and a female flower comprising a flask-shaped pistil. The order Lemnaceae to which they belong is regarded as representing a very reduced type nearly allied to the Aroids. It is represented in Britain by four species of Lemna, and a still smaller and simpler plant, Wolffia, in which the fronds are only one-twentieth of an inch long and have no roots.
1, Lemna minor (Lesser Duckweed) nat. size.
2, Plant in flower.
3, Inflorescence containing two male flowers each of one stamen, and a female flower, the whole enclosed in a sheath.
4, Wolffia arrhiza.
(2, 3, 4 enlarged.)