Invasive Alien Species in Northern Ireland

Myriophyllum aquaticum, Parrot's Feather

Myriophyllum aquaticum
© Graham Day
Myriophyllum aquaticum
Click on map to enlarge
Myriophyllum aquaticum (Vell.Conc.) Verdc., Camb.
 
Introduction
Parrot's feather is an aquatic plant which is a potential threat to lakes and ponds. In some parts of Great Britain this is now a serious nuisance, but so far it has failed to spread in Northern Ireland.
 
Description
Parrot's feather is a foreign species of water milfoil (Myriophyllum spp.) of which there are three species native to Ireland. All water milfoils are aquatics with most of the plant underwater and the leaves finely divided, but with the flowering spike held above the water. Flowers are small and insignificant.
Parrot's feather is a little different from the three natives in that it has male and female flowers on separate plants (but only female plants are reported in the British Isles), and it can grow on dry ground as well as in ponds. The leaves produced out of water are less divided than the submerged ones and have a characteristic feather-like appearance.
 
Country of origin
South America.
 
Location in Ireland
So far, this plant appears to be found only at one site, a flooded clay pit, in the Ards Peninsula, County Down. The plant is available for sale at a number of garden centres.
 
Life cycle
Because all British and Irish plants are female, this plant can only spread vegetatively. The stems are brittle and fragments will grow into mature plants. Propagation by or for garden centres is by fragmentation. The plant is also rhizomatous, and will form new shoots from the rhizome. It can choke ponds rapidly with excessive growth. The excess material, if discarded into other water bodies, can spread the plant around.
 
Wildlife and habitat impacts
The primary effect of this plant is caused by its out competing native water plants.
 
Key vectors
Potentially, spread could be by plant fragments attached to footwear, fishing kit, and possibly (although unproven) wading birds' feet. The Centre for Aquatic Plant Management at CEH Wallingford, suggests that fragments of the plant in the soil of other purchased plants such as water lilies could be a source of infestation.
 
Further information
Links
Centre for Aquatic Plant Management, CEH, Wallingford - advice on identification and control www.capm.org.uk
Royal Horticultural Society - general information and advice on invasive alien plants, including parrot's feather http://www.rhs.org.uk/Learning/research/documents/c_and_e_nonnative.pdf
Royal Botanic Gardens Kew; information sheet T4 on invasive species
www.rbgkew.org.uk/ksheets/pdfs/t4invasive_species.pdf
 
See the Invasive Species Ireland web site for further information -
http://www.invasivespeciesireland.com/mostunwanted/
 
Text written by:
Paul Hackney, Keeper of Botany, Ulster Museum