Biddy-biddys (piripiri in Māori) is a genus of some 50 species mostly found in Australia, New Zealand and South America, although one made it to Hawaii and one to California. On the other hand, some of the Acaenas have managed to become weeds in other parts of the world, which is highly unusual for a NZ species. Their spread is aided by the long arrow-head barb on the seeds, which attach to fur or socks. Presumably they also attach to feathers, since the only native land mammals in New Zealand were three species of bat, and one of those is probably extinct.