Some New Zealand plants overseas are garden escapees, having spread from cultivation and run wild. New Zealand flax, cabbage trees, various species of hebe, pittosporum, olearia, carex, and many others have become established in this way in Australia, Britain, the United States and elsewhere.
The New Zealand flax once grown commercially on St Helena, in the South Atlantic, continues to grow wild there – so vigorously that is displacing the struggling local native plants and is regarded as a threat. Karaka (Corynocarpus laevigatus), planted in Hawaii for afforestation purposes in the 1920s, also remains there as a serious weed.
Some plants have been carried abroad in other ways. Four species of the mat-forming piri-piri or ‘biddy-bid’ (Acaena) have been carried in exported wool and are now growing as weeds in parts of the United States and in Britain, especially near old woollen mills.
Other species have been carried abroad unnoticed in potted plants. Several species of Epilobium, which are hardly noticed at home in New Zealand, have become established across Europe, and are now gaining a foothold in North America. One of them, Epilobium brunnescens, known as ‘New Zealand willowherb’ in Britain, has become an aggressive invader, listed among the 20 worst introduced weeds there.