Azolla

From Gardening Wiki

Azolla

Azolla is a small, floating aquatic plants (ord. Rhizocarpese), of which the only one in cultivation is caroliniana, an attractive Fern-like little plant which hardly rises above the surface of the water and covers it with a carpet of green, which changes in summer to a bronze colour.

It is perfectly hardy, and may be grown in still water outside, or in a basin or aquarium indoors. The Azolla makes a beautiful microscopic object. It increases rapidly, and needs no care beyond placing it on the surface of shallow water at first, with the root fibres downward. It requires no soil.