Azolla filiculoides

Tracheophyta PteropsidaAzollaceaeAzollaAzolla filiculoides


A floating fern of canals, ditches, ponds and sheltered bays in lakes and rivers. It is most frequent in calcareous water, or near the sea. It reproduces vegetatively, often producing dense mats, and sporocarps are not uncommon. Generally lowland, but reaching 450 m above Rydal Water (Westmorland).



World Distribution

Native of western N. & S. America; widely naturalised in temperate and southern Europe and elsewhere.

Broad Habitats

Light (Ellenberg): 7

Moisture (Ellenberg): 11

Reaction (Ellenberg): 8

Nitrogen (Ellenberg): 8


Salt Tolerance (Ellenberg): 0

January Mean Temperature (Celsius): 4

July Mean Temperature (Celsius): 16

Annual Precipitation (mm): 774

Length: 1

Perennation - primary


Life Form - primary

Perennial hydrophyte (perennial water plant)



Clonality - primary

Fragmenting as part of normal growth

Count of 10km squares in Great Britain: 660

Count of 10km squares in Ireland: 21

Count of 10km squares in the Channel Isles: 9

Atlas Change Index: 2.76

Distribution information

JNCC Designations


PLANTATT - Attributes of British and Irish plants. (.zip 1455KB) This dataset was compiled and published in 2004, and last updated in November 2008. Download includes an Excel spreadsheet of the attributes, and a PDF explaining the background and nomenclature. Note that the PDF version is the booklet as published, whereas the Excel spreadsheet incorporates subsequent corrections. A hardcopy can be purchased from the Centre for Ecology and Hydrology.

Atlas text references

Atlas (15c)
FNAEC (1993b)
Jalas & Suominen (1972)
Bangerter EB, Cannon JFM, Jermy AC
1978.  Ferns and their allies. The Island of Mull: a survey of its flora and environment. :12.1-12.7.
Preston CD, Croft JM
1997.  Aquatic plants in Britain and Ireland.