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Azolla filiculoides facts for kids

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Azolla filiculoides
Azolla filiculoides0.jpg
Zoomed picture of Azolla filiculoides
Conservation status

Secure (NatureServe)
Scientific classification
  • Azolla arbuscula Desv.
  • Azolla caroliniana Willd.
  • Azolla japonica Franch. & Sav.
  • Azolla magellanica Willd.
  • Azolla microphylla Kaulf.
  • Azolla pinnata var. japonica (Franch. & Sav.) Franch. & Sav.
  • Azolla squamosa Molina

Azolla filiculoides (water fern) 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. It harbors the diazotrophic organism, Nostoc azollae, in specialized leaf pockets. This ancient symbiosis allows N. azollae to fix nitrogen from the air and contribute to the fern's metabolism.

Fossil records from as recent as the last interglacials are known from several locations in Europe (Hyde et al. 1978).

Azolla filiculoides was one of the first two fern species for which a reference genome has been published.


The only sure method of distinguishing this species from Azolla cristata (long incorrectly known as A. caroliniana) 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 (two-celled) in A. cristata.


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.


Ireland: Introduced into Clandeboye Lake, Co. Down.


  • Azolla filiculoides
  • Azolla filiculoides (pink-tinged) growing together with Lemna minor duckweed
  • Single Azolla filiculoides plant showing the roots
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