Banana passionfruit (Passiflora tripartita)
A large, vigorous woody climber, banana passionfruit scrambles into tree canopies and stifles its host. A single plant can grow to cover the area of a house. The plant has three-fingered leaves, tendrils, long pink hanging flowers the year round, and pendulous, banana-shaped fruit in winter. The fruit turns yellow when ripe.
Banana passionfruit grows at forest edges in the North Island and in warmer parts of the South Island. Its seeds are spread by possums, wild pigs and birds. It is partly held in check by garden snails, which ring-bark the lower stems. Originally from Brazil, it was first noticed growing wild in New Zealand in 1958. Banana passionfruit is an aggressive weed on many Pacific islands.
Blackberry (Rubus fruticosus)
The first British settlers brought blackberry to New Zealand, and more plants have come from Australia and the USA. The plant quickly spread, and 19th-century farmers declared it the most harmful weed in New Zealand. It was jokingly said that there were only two blackberry plants on the West Coast – one running along each side of the railway line.
At least 19 varieties of blackberry grow throughout New Zealand. Its roots can spread for many metres, making mature plants difficult to eradicate. Fruit-eating birds such as blackbirds and quail spread seeds along the roadside, in bush margins, clearings and in regenerating forest.
In 1925 the New Zealand government vainly offered a £10,000 reward (about $800,000 in 2006) for a method to stamp out blackberry. Goats were sometimes used to trample it down – mostly without success. It was only when hormone sprays were invented in the 1940s that farmers could control blackberry. It still remains a serious pest in scrubland and forest reserves in Northland, Nelson, the West Coast and elsewhere.
Climbing asparagus (Asparagus scandens)
Also known as snakefeather, this is a scrambling, shade-tolerant climber with feathery leaves and a tuberous root. Introduced from Africa in the late 1940s, the plant has spread in frost-free areas of New Zealand as far south as Banks Peninsula. It smothers native shrubs and saplings, and stops native seedlings from regenerating. The plant is still spreading in the warmer parts of the country.
German ivy (Senecio mikanioides)
German ivy is a yellow-flowered scrambler with stems up to 5 metres long. It may extend along the margins of bush, smothering shrubs and preventing native plants from regenerating. It is a problem in native plant reserves and cutover forest in the central North Island, Wellington, Nelson and elsewhere.