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..
Minute moss-like reddish or green floating plants, with pinnately branched stems covered with minute imbricated 2-lobed leaves, and emitting rootlets beneath. Sporocarps of two kinds borne in the axils of the leaves, the smaller ovoid or acorn-shaped, containing a single megaspore at the base and a few corpuscles above it whose character is not fully known, the larger globose, producing many pedicelled sporanges, each containing several masses of microspores which are often beset with a series of anchor-like processes of unknown function. [Greek, signifying killed by drought.]
About 5 species of wide geographic distribution. Type species: Azolla filiculoides Lam.
Azolla caroliniana Willd. Sp. PI. 5: 541. 1810.
Plants greenish or reddish, deltoid or triangular-ovate in outline, pinnately branching, sometimes covering large surfaces of water. Leaves with ovate lobes, their color varying somewhat with the amount of direct sunlight, the lower usually reddish, the upper green with a reddish border. Megaspores minutely granulate, with three accessory corpuscles; masses of microspores armed with rigid septate processes.
Floating on still water, Ontario and Massachusetts to British Columbia, south to Florida, Arizona and Mexico. Also in tropical America. Naturalized in lakes on Staten Island, N. Y.