Water fern

Azolla filiculoides


Photo credit: ©CABI-2008
Azolla filiculoides
  • Still and slow flowing freshwater bodies

  • Azolla is a floating aquatic fern that is almost moss-like in appearance. It is bright green in colour with a noticeable fine red border round each leaf. Leaves up to 2.5 cm. Often acquires a rusty red colouration in winter, or when stressed. It is not tolerant of turbulence or waves, and is usually flushed out of fast-flowing rivers and streams. It consists of a branched stem with attached leaves divided into two lobes. The upper lobes floating on the water surface, c.1-1.5mm across, overlapping and concealing the stem. The lower, submerged lobes are larger but not overlapping so that the stem is visible. Individual roots originate from the lower surface of the stem at the junctions with the side branches. Sori are in one or two pairs on the lower lobe of the first leaf of a lateral branch.
  • Download N.I.E.A. ID guide

Origin and Distribution:
  • Western North America from Washington State to Mexico. Now found in continental Europe, the United Kingdom and Ireland.

  • Dense rafts of Azolla can accumulate, especially under the influence of winds and currents. These will reduce light levels penetrating beneath the surface of the water to waterweeds and algae, which could die off, seriously reducing oxygenation in the water.

How did it get here?
  • Garden and aquaria trade

Is it found in Ireland or Northern Ireland?
  • It is found across numerous sites across Ireland and Northern Ireland,
  • More information can be found at NBDC and NBN Atlas NI.

You can help by reporting any sightings:

Static Distribution Map as of December 2019 - Courtesy of CEDaR

Prevent Spread:
  • Record sightings.
  • Promote native species and biodiversity - use alternative, native plants
  • Know what you are buying/growing and source native Irish seed and plants
  • Do not swap plants and cuttings
  • Clean plants before adding to ponds (dispose of water away from water courses)
  • Follow control advice and watch out for hitchhikers - inspect new imported purchases for invasive pest and pathogens
  • Clean equipment before moving between waterbodies - see Check Clean Dry for further information.
  • Never collect plants from the wild
  • Safe disposal of plant material and growing media

Current Legislation Position:
  • Azolla filiculoides is listed in Schedule 9 of the Wildlife (Northern Ireland) Order 1985 and as such, under Article 15 it is an offence to plant or otherwise cause this species to grow in the wild.

Species Related Files:

Invasive Species Ireland

Invasive Species Ireland