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 Acaena novae-zelandiae foliage and various fruiting stages | ||||||||||||||||||
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Acaena is a genus of about 100 species of perennial herbs and subshrubs in the Rosaceae, native mainly to the Southern Hemisphere, notably New Zealand, Australia and South America, but with a few species extending into the Northern Hemisphere, north to Hawaii (A. exigua) and California (A. pinnatifida).
The leaves are alternate, 4-15 cm long, and pinnate or nearly so, with 7-21 leaflets. The flowers are produced in a tight globose inflorescence 1-2 cm diameter, with no petals. The fruit is also a dense ball of many seeds; in many (but not all) species the seeds bear a barbed arrowhead point, the seedhead forming a burr which attaches itself to animal fur or feathers for dispersal.
- Selected species
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Invasive species
Some species have been introduced accidentally to other areas, attached to sheep's wool, and have become invasive species. A. novae-zelandiae, the bidibid from New Zealand, is the most commonly encountered species in Great Britain, where it is often abundant on coastal sand dunes, crowding out native vegetation and creating an often painful nuisance with the barbed burrs. In California, A. pallida, from New Zealand and southeast Australia, is similarly a problem species.