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. [illustration: 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.)]