Reproductive Ecology of Pseudowintera (Winteraceae)

Abstract

Pseudowintera, endemic to New Zealand, is a member of the primitive dicotyledonous family Winteraceae. The ecological aspects of reproduction in Pseudowintera are traced from the production of pollen and ovules, through pollination, incompatibility, fruit formation and seed set, to seed dispersal and germination. Pseudowintera has small inconspicuous flowers that are long-lived and lack floral movements. The flowers attract a diverse assemblage of insect visitors — the typical situation of plants in New Zealand. Flies were among the important pollinators for the two species, P. axillaris and P. colorata, which were studied intensively. In addition, thrips were found as pollinators of P. axillaris and associated lowland trees. The larvae of a geometrid moth are restricted in their feeding to the foliage and flowers of Pseudowintera, and also serve to pollinate P. colorata, a previously unknown plant-insect relationship. Evidence is presented to show that Pseudowintera may have a gametophytic incompatibility system expressed within the ovule. In nature a low proportion of flowers become fruits and it is suggested that the non-fruit-forminq flowers have a reproductive effort via pollen. On the basis of pollen: ovule ratios and fruit/seed set data, two breeding strategies are proposed for the Winteraceae. The seeds of Pseudowintera are bird-dispersed, an adaptation which evolved well after the Winteraceae were present on New Zealand P. traversii reproduces primarily by vegetative means and possible reasons for this are suggested. Hybridization is examined with emphasis on artificial interspecific pollinations and an evaluation of previous reports of natural hybrids.