This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol1", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Duckweed Family. Minute perennial floating aquatic plants, without leaves or with only very rudimentary ones. The plant body consists of a disc-shaped, elongated or irregular thallus, which is loosely cellular, densely chlorophyllous and sometimes bears one or more rootlets. The vegetative growth is by lateral branching, the branches being but slightly connected by slender stalks and soon separating. In the autumn these disconnected branches fall to the bottom of the ditch or pond, but rise and again increase in size in the spring. The inflorescence consists of one or more naked monoecious flowers borne on the edge or upper surface of the plant. Each flower commonly consists of but a single stamen or a single flask-shaped pistil. The anther has two to four pollen-sacs, containing spherical minutely barbellate grains. The pistil is narrowed to the funnel-shaped scar-like stigmatic apex, and produces 1-6 erect or inverted ovules. The fruit is a 1-6-seeded utricle.
Comprises the smallest of the flowering plants and contains 4 genera and about 26 species. Thallus with one root or several.
Thallus thick, globose to subcylindric.
Thallus thin, ligulate.