Other formats

    TEI XML file   ePub eBook file  

Connect

    mail icontwitter iconBlogspot iconrss icon

Forest Vines to Snow Tussocks: The Story of New Zealand Plants

Branch Parasites

Branch Parasites

These all contain chlorophyll so are only partly dependent on their hosts for organic nutrients. All but one of the New Zealand parasites in this category belong to two largely tropical families — Viscaceae and Loranthaceae, collectively referred to as mistletoes. In the first the flowers are small and inconspicuous, in the second they are much larger and often brilliantly coloured.

Three small species of Korthalsella represent the Viscaceae. All have vestigial leaves and strongly jointed stems, which in K. lindsayi and K. clavata are strongly flattened and in K. salicornioides, cylindrical. K. salicornioides is found throughout the country while K. lindsayi and K. clavata are found from the central North Island southwards. Both parasitise a wide range of shrubs and small trees.

The New Zealand species in the family Loranthaceae are all green-leaved, freely branching shrubs of up to one metre in diameter. Currently all these species are referred to a number of small genera,56 with one exception endemic to New Zealand, although formerly some were included in the tropical genera Elytranthe and Loranthus. Tupeia antarctica is the only species of a genus restricted to New Zealand. Each plant is attached to a ball-like mass, which is a combination of the parasite haustorium and the host tissues. Tupeia is found throughout the country and attacks a wide range of both native and introduced shrubs and small trees, and occasionally other branch parasites.

Peraxilla colensoi and P. tetrapetala mostly parasitise Nothofagus species in both islands. They have bright red flowers which form eye-catching page 95patches of colour against the dark green beech foliage. The orange flowers of Alepis flavida, seen mostly on beech trees, are also very attractive. Trilepidea adamsii, with reddish cream flowers, is restricted to the northern Coromandel Peninsula and adjacent localities and was last recorded in the 1960s. Ileostylus micranthus has small green flowers and yellow berries. It is widespread in New Zealand and Norfolk Island and has as its hosts a range of shrubs, small trees and, sometimes, conifers both native and introduced. The species of all these genera except Tupeia send out roots over the bark surface which form secondary haustoria at intervals. Ileostylus alone can form new leafy shoots from its roots.

The branch parasites have berries which are eaten by birds and the seeds deposited on tree branches. The seeds are attached to bark by a sticky secretion. Some branch parasites elsewhere have explosive fruits, which shoot the seeds for several metres. This has been observed in the New Zealand species of Korthalsella.

The remaining parasite in this category is Cassytha pubescens. A twining vine as well as a parasite, it is quite different from the rest. Its seeds
Figure 59 Tangled thread-like stems of the leafless parasite Cassytha pubescens on manuka (Leptospermum scoparium). Near North Cape, North Island.Photo: J. W. Dawson.

Figure 59 Tangled thread-like stems of the leafless parasite Cassytha pubescens on manuka (Leptospermum scoparium). Near North Cape, North Island.
Photo: J. W. Dawson.

page 96germinate in the ground and the slender yellow green primary stem with rudimentary leaves rotates in anti-clockwise direction winding tightly around any stems it encounters. At frequent intervals haustoria penetrate the host. The stems of the Cassytha branch freely, but remain slender, festooning the shrub hosts with tangled stringlike masses (Fig. 59). This species is restricted to the northern half of the Northland peninsula where it grows on shrubs and particularly manuka (Leptospermum scoparium). It is surprising to find that Cassytha belongs to the Lauraceae, a family which otherwise consists of mostly tropical and subtropical trees including the species of Beilschmiedia and Litsea in New Zealand. Our species of Cassytha is also found in Australia and there are other species there and in Melanesia, tropical Asia and South Africa.