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Giant Gunnera

(Gunnera tinctoria)

Also commonly known as commonly known as Giant Rhubarb, Gunnera tinctoria is an introduced species that has become invasive in the west of Ireland. Although the exact date of its introduction to Ireland is unknown, it was first recorded in the wild in Ireland in 1939 on Achill Island. Pollen analysis suggests that it could have been present on Achill Island for 70-100 years  

Identification

  • Large herbaceous perennial which can grow up to 2 meters tall
  • Leaves of up to 2 meters in diameter
  • It is deciduous with the leaves dying off in autumn (October) leaving the large brown rhizomes exposed
  • Inflorescence development occurs early in the spring  with the fruits maturing in late summer/early autumn.

Giant Gunnera

Giant Gunnera

Reproduction

  • It can reproduce by both sexual (seed) and asexual (vegetative) means.
  • Large numbers (up to 250 000 seeds per mature plant) of red or orange seeds are produced. 
  • Small fragments of the rhizome have the potential to establish new plants.

Issues

To date there has not been a detailed assessment of the impact of Gunnera on native ecosystems. Previous studies indicate there is a reduced number of native species growing underneath large colonies. In grassland sites it was found that former species-rich sites were replaced with a sparse cover of dicotyledonous species not found in un-colonised sites. Of particular concern are impacts associated with peat bog and waterside vegetation, as large dense colonies can rapidly dominate and displace important native species. On coastal cliffs, the main impact is caused by increasing the threat of erosion and loss of maritime species.

Giant Gunnera flowering

Giant Gunnera distribution

Treatment

Chemical control can be effective in treating large areas and is generally considered efficient and cost effective. The major drawback of using chemicals is the impacts they can have on the environment, affecting not only the target species but other species in the neighboring area. The use of chemical control on Gunnera has been investigated both in Ireland and New Zealand. Further experimentation and monitoring on the use of chemical control methods is currently being carried out on Achill Island.

Contact us

Japanese Knotweed Ireland Ltd.
+353 21 2019732 / +353 86 3620047
info@japaneseknotweedireland.ie

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