Azolla filiculoides


Azolla filiculoides is a species of Azolla, 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.
Fossil records from as recent as the last interglacials are known from several locations in Europe.
Azolla filiculoides is one of just two fern species for which a reference genome has been published.

Identification

The only sure method of distinguishing this species from Azolla cristata is to examine the trichomes on the upper surfaces of the leaves. Trichomes are small protuberances that create water resistance. They are unicellular in A. filiculoides but septate in A. cristata.

Cultivation

The species has been introduced to many regions of the Old World, grown for its nitrogen-fixing ability that may be used to enhance the growth rate of crops grown in water, such as rice, or by removal from lakes for use as green manure. It has become naturalized, sometimes also an invasive species, in several regions, including western Europe, southern Africa, tropical Asia and New Zealand.

Distribution

Ireland: Introduced into Clandeboye Lake, Co. Down.

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