Azolla filiculoides (Water Fern) is a species of the family Azollaceae, native to warm temperate and tropical regions of the Americas as well as most of the old world including Asia and Australia. It is a floating aquatic fern, with very fast growth, capable of spreading over lake surfaces to give complete coverage of the water in only a few months.
Each individual plant is 1-2 cm across, green tinged pink, orange or red at the edges, branching freely, and breaking into smaller sections as it grows. It is not tolerant of cold temperatures, and in temperate regions it largely dies back in winter, surviving by means of submerged buds. Like other species of Azolla, it can fix nitrogen from the air.
The species has been introduced to many regions of the Old World, grown for its nitrogen-fixing ability which can be utilised to enhance the growth rate of crops grown in water like rice, or by removal from lakes for use as green manure. It has become naturalised, sometimes also an invasive species, in several regions, including western Europe, southern Africa, tropical Asia, Australia (where it is considered native), and New Zealand.
This post is part of the Friday Greens meme.