EXPLOSIVE FLOWERING, NECTAR PRODUCTION, BREEDING SYSTEMS, AND POLLINATORS OF NEW-ZEALAND MISTLETOES (LORANTHACEAE)

The six New Zealand loranthaceous mistletoes fall into two groups base d on pollination biology. Four (Alepis flavida, Peraxilla colensoi, P. tetrapetala, and Trilepidea adamsii) are bird pollinated with hermaph rodite flowers while the other two (Ileostylus micranthus and Tupeia a ntarctica) are dioecious or sub-dioecious and insect pollinated. We pr ovide data on the pollination biology of the five extant species (Tril epidea is extinct). The two Peraxilla species and Trilepidea have rece ntly been shown to have explosive flowers. Here we show that Alepis ha s weakly facultatively explosive flowers. The world distribution of ex plosive mistletoe flowers suggests that the syndrome has arisen a numb er of times independently within the family, and is found in about hal f the putatively ancestral genera. The principal avian visitors to the bird-pollinated species were tui and bellbirds; introduced species ar e numerically unimportant as pollinators. The nectar production schedu les of Alepis and Peraxilla encourage single-visit pollination as litt le nectar is produced after the flowers open. However, when bird densi ties are high, buds of Peraxilla may be forced open prematurely, encou raging multiple visits. Alepis is highly self-compatible and its flowe rs achieve good seed set in the field even when all pollinators are ex cluded by mesh bags, partly because pollen contacts the already-recept ive stigma before the bud opens. Unvisited Peraxilla buds do not open, but their morphology allows a low level (11-22%) of self-pollination in the bud. The sex ratio of Tupeia at Wainui (Banks Peninsula) was 3: 1 female:male, while Ileostylus at Wakefield (Nelson) was subdioecious with a 2.5:1:1 female:male:hermaphrodite ratio. Hermaphrodite Ileosty lus plants set seed even when pollinators are excluded, so self-pollin ation is possible in this species. Results suggest different species v ary in their susceptibility to pollen limitation affecting reproductio n. The insect-pollinated species have unspecialized pollination syndro mes and are probably adequately pollinated by native and/or introduced insects; Ileostylus is also self-compatible. The bird-pollinated spec ies are more susceptible with specialised pollination systems dependin g principally on endemic birds, but the effect is reduced in Alepis as its flowers can open themselves and it achieves good seed set even wh en pollinators are excluded. Peraxilla spp. seem most at risk with obl igately-explosive flowers and only low seed set without pollinators. H istorical declines in the North Island have been greatest in the speci es with the most exacting pollination requirements. Long-term conserva tion of these mistletoes will require conservation of tui and/or bellb irds.