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

Root Parasites

Root Parasites

Dactylanthus taylorii54 (Fig. 58) is a complete parasite attached to the roots of a range of mostly small tree species in lowland to montane forest throughout the North Island. It is not readily observable as only the reddish-brown, scaly inflorescences appear above the ground. The strange appearance of the flower heads which apparently arise directly from the ground, led the Maori to give the name pua reinga (flower of the Underworld) to this species.

Apparently the embryo root of a Dactylanthus seed penetrates the slender root of a suitable host, then gradually expands into a tuber-like structure which eventually surrounds the host root. The terminal portion of the host root then dies away. The 'tuber' continues to enlarge and the end of the host root enlarges with it into a disc-like form. Both can attain a diameter of up to 30 cm. The tuber has a flattened ball-like shape and is covered with hard warty protuberances. Inflorescence buds originate between these, bearing male flowers on some plants, female flowers on others. The flowers have a strong sweet perfume which is attractive to flies. The junction between host and parasite is not flat, but formed into radiating grooves, v-shaped in section. It has been found that if the host/parasite mass is boiled, the parasite can be removed exposing the expanded, fluted ends of the host roots. These 'wooden roses', as they are called, are prized as curios. Dactylanthus is restricted to New Zealand but belongs to a largely tropical and subtropical family.

Although Mida salicifolia55 is a root parasite on a wide range of trees including kauri, unlike Dactylanthus it does not advertise the fact. It is a small tree with narrow, green willow-like leaves in one variety and page 94rather broader leaves in the other. It is found in lowland forests throughout the North Island, but becomes uncommon in the south of its range. The only other species of the genus is restricted to the Juan Fernandez islands near Chile.

Other root parasites in New Zealand are found in open subalpine and alpine sites. Exocarpus bidwillii is leafless with stiff, yellow-green stems branching in a coral-like fashion. Other species of the genus are small trees and shrubs of the tropics (Madagascar, Australia, Malaysia, New Caledonia, Polynesia).

Like Mida, the fifteen green-leaved, mostly alpine herbs of the genus Euphrasia55 in New Zealand give no hint of their parasitic behaviour. The genus is widespread in temperate regions of both hemispheres.