|Zoomed picture of Azolla filiculoides|
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.
Azolla filiculoides is one of just 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 which can be utilized 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 naturalized, sometimes also an invasive species, in several regions, including western Europe, southern Africa, tropical Asia, Australia (where it is considered native), and New Zealand.
Ireland: Introduced into Clandeboye Lake, Co. Down.
- In: Encyclopédie Méthodique, Botanique 1(1): 343. 1783. "Name - Azolla Lam". Tropicos. Saint Louis, Missouri: Missouri Botanical Garden. Retrieved February 19, 2010.
Annotation: a sp. nov. reference for Azolla filiculoides
Type Specimens HT: Azolla filiculoides
- Hussner, A. (2006). "NOBANIS -- Invasive Alien Species Fact Sheet -- Azolla filiculoides" (PDF). Online Database of the North European and Baltic Network on Invasive Alien Species. Heinrich Heine University, Düsseldorf. Retrieved February 19, 2010.
- Li, Fay-Wei; Brouwer, Paul; Carretero-Paulet, Lorenzo; Cheng, Shifeng; de Vries, Jan; Delaux, Pierre-Marc; Eily, Ariana; Koppers, Nils; Kuo, Li-Yaung (2018-07-02). "Fern genomes elucidate land plant evolution and cyanobacterial symbioses". Nature Plants. 4 (7): 460–472. doi:10.1038/s41477-018-0188-8. ISSN 2055-0278.
- Evrard, C.; Van Hove, C. (2004). "Taxonomy of the American Azolla Species (Azollaceae): A Critical Review". Systematics and Geography of Plants. 74 (2): 301–318.
- Hackney, P. (Ed) 1992. Stewart & Corry's Flora of the North-east of Ireland. Third Edition. Institute of Irish Studies & The Queen's University of Belfast. ISBN 0-85389-446-9(HB)
- Hyde, H. A., Wade, A. E., & Harrison, S. G. (1978). Welsh Ferns. National Museum of Wales. ISBN 0-7200-0210-9.
- Sainty, G. & Jacobs, S. (2003) Waterplants in Australia. Sainty and Associates, Potts Point, Sydney, Australia. ISBN 0-9581055-1-0
- Media related to Azolla filiculoides at Wikimedia Commons
- "Azolla filiculoides". Germplasm Resources Information Network (GRIN). Agricultural Research Service (ARS), United States Department of Agriculture (USDA).
- Flora of North America: Azolla filiculoides
- USDA Plants Profile: Azolla filiculoides
- Plants for a Future: Azolla filiculoides
- NSW Flora Online: Azolla filiculoides