Pirri-pirri bur

Acaena spp.

Overview

Photo credit: © Krzysztof Ziarnek
 Acaena ovalifolia & Acena novae-zelandiae
Common names:
  • A. ovalifolia - Two spined acaena, 
  • A. novae-zelandiae - Biddy-biddy, Biddy-widgee, red bidibid, New Zealand bur

Habitat:
  • Woodland, forestry plantations and tracks, sand dunes, heaths, cliffs, railway embankments and other bare ground

Description:As both species have a similar appearance species identification can be difficult. 
  • A. ovalifolia; has a woody stem, its leaves pinnate, 5-12cm long. 3-5 pairs of finely wrinkled leaflets (underside green) 10-13mm long, 1.5 to twice as long as wide. Flower is spherical, up to 4cm in diameter, 2 spines per fruit (8-10mm long), barded and red.  
  • A. novae-zelandiae; woody stem only at base, 2-6 pairs of leaflets. Deeply toothed (7-12 on each side), smooth oblong-shaped, bright green on upper surface, paler underneath. Greenish-white, spherical head of small flowers up to 4 spines per flower (6-10mm long). Seed head is a spherical burr with 4 red barded spines.
  • Download N.I.E.A. ID guide
 
Origin and Worldwide Distribution:
  • Native to South America (A. ovalifolia) is present in United Kingdom, Ireland, 
  • Native to New Zealand and south-east Austraila (A. novae-zealandiae) is present in United Kingdom, Ireland,  Denmark and United States of America.

Potential or known impacts:
  • Forms a dense and trample resistant mat which will displace native species. Once established it is very difficult to eradicate.

How did it get here?
  • Originally imported as a ornamental plant. Escapes and releases from garden collection have resulted in this plant becoming established. Reproduces from seed which sticks to clothes (socks and trouser legs in particular) and animals' fur.
Acaena ovalifolia seed
Acaena novae-zealandiae seed
 
Is it found in Ireland or Northern Ireland?
You can help by reporting any sightings:
Further Resources: 
Methods for Prevention:
  • Report any sightings
  • All species of Acaena are listed under Schedule 9 of The Wildlife (Northern Ireland) Order 1985 and as such it is an offence to plant in the wild.  
  • Do not plant this species – plant native species instead.
  • Do not take or give cuttings from wild or cultivated plants.
  • Know what you are growing.
  • Never collect plants from the wild.
  • Check clothing, equipment and animal fur for seeds before leaving an area where Acaena spp. is established. 
  • Safely dispose of plants and growing media.

Species Related Files:

Invasive Species Ireland

Invasive Species Ireland