The ecology of Dactylanthus taylorii and threats to its survival
- New Zealand Forest Research Institute Ltd, Private Bag 3020, Rotorua, New Zealand
Dactylanthus taylorii, a root parasite in the family Balanophoraceae, is New Zealand's only fully parasitic flowering plant. It grows attached to the roots of a wide range of hardwood trees and shrubs, often in fire-induced secondary forest on the margin of podocarp-hardwood forest. It is inconstantly dioecious with a skewed sex ratio of approximately 5:1 male to female inflorescences. The inflorescences, especially the males, contain a large quantity of nectar, up to 1.6 mi, and can produce 0.5 mi per day for 10 days. The morphology of the inflorescences, the quantity and chemistry of the nectar, time-lapse video monitoring and other evidence suggest that the Dactylanthus flowers are adapted for pollination by short-tailed bats. Ship rats are also effective pollinators but occasionally destroy the inflorescences. Kiore completely destroyed all the inflorescences observed on Little Barrier Island in 1992 and 1993, although some seed was found there in 1991. Dactylanthus plants have been successfully cultivated by sowing seeds close to the roots of broadleaf plants. Germination was very slow with the highest rates occurring nearly five years after the seed was sown. Further research is needed to clarify the role of fungal hyphae found inside the cells of a young plant and that of the sheath processes which may assist vegetative reproduction. Video monitoring provided evidence that the introduced possum, by browsing the inflorescences, threatens the survival of Dactylanthus at most North Island sites. Where possums were present, and the plants unprotected, almost all the inflorescences were browsed. Adult plants at the main study site had a half-life of only 8.5 years. Conservation management to ensure the survival of Dactylanthus will require protection of the plants from possums, rats and humans and adequate areas of secondary forest containing abundant host plants.