This seemingly innocent question has already roused strong passions in Australia, and plant ecologist Prof Angela Moles, of Sydney, was recently criticised as ''a witch'' for some of her comments.
Prof Moles, who grew up in the North Island and has dual New Zealand-Australian citizenship, discussed exotic plants again during the annual Tennant Lecture in Dunedin yesterday.
Prof Moles, who is director of the Evolution and Ecology Research Centre at the University of New South Wales, said some of the hostility she had encountered arose from the challenge her research posed to the traditional way of classifying plants as exotic (imported), native (indigenous to a country) or endemic (found only in that country).
''The idea that an introduced weed could become a new native species is very challenging for many people, especially those with a strong interest in conservation,'' she said.
She points to the South African beach daisy, an exotic flowering plant introduced to Australia in the 1930s.
After growing in more challenging conditions in Australia, strong winds and shifting sands had sparked rapid adaptive change, and evolution into a new endemic species.
A study she had conducted in Australia of 23 small herbaceous exotic plants, including some weeds and clovers, showed 70% (16) had undergone significant change and the beach daisy was a new endemic.
A study of 18 small exotic plants in New Zealand showed a lower rate of adaptive change (about 27%).
Among the five plants that had changed, sticky mouse-ear chickweed and buck's horn plantain were now shorter, and hop clover, staggerweed and windmill pink had smaller leaves.
New Zealand had more than 2000 introduced plant species, and if some kept changing in response to their new environment, they would eventually ''become new species too, whether we like it or not''.
A key decision was whether to ''try to eradicate these new species'' or to accept them as a new part of our native biodiversity.
