Water fern

Azolla filiculoides

Overview

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

Description:
  • 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 Northern Ireland.

Impacts:
  • 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 Northern Ireland?
  • It is found across numerous sites across Northern Ireland,
  • More distribution information can be found at  NBN Atlas NI.

You can help by reporting any sightings: @ the Centre for Environmental Data & Recording (CEDaR) - Or via the iRecord App.
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 (Northern Ireland only):
  • 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.

Water fern research:

Effect of population density of the Azolla weevil (Stenopelmus rufinasus) on the surface cover of the water fern (Azolla filiculoides) in the UK

For further queries, you can contact the Invasive Non Native Species (INNS) Team in the Northern Ireland Environment Agency on 028 9056 9558 or Email: invasivespecies@daera-ni.gov.uk

Azolla filiculoides Research/Bio Control


 
  • Stenopelmus rufinasus, an Azolla-feeding weevil, was introduced accidentally to the UK, most likely as a stowaway on A. filiculoides. It was first recorded in England in 1921 and has survived in nature ever since, feeding on Azolla and providing background control of the weed, typically unnoticed
  • In the mid-2000s, CABI investigated the potential to mass rear and redistribute S. rufinasus to control these outbreaks. In England and Wales S. rufinasus is recognized as ordinarily resident and in Scotland the weevil is released under licence. CABI now ships the weevil throughout the summer months to customers affected by Azolla
  • To date this method has not been tested in Northern Ireland
  • Over a period of two to three months, S. rufinasus feeds and reproduces extensively and brings the Azolla under control. It can be so efficient that it effectively eliminates its entire food source and adults must then fly in search of further Azolla infestations, leaving clear water bodies
  • Biocontrol is recognized as the best approach for managing Azolla where the weed and weevil are present, and CABI has demonstrated the effectiveness of the weevil in trials in the UK, Netherlands and Belgium and identified S. rufinasus damaging Azolla in the field in France
 
 

Species Related Files:

Invasive Species Northern Ireland

Invasive Species Northern Ireland