Pollination processes in Idiospermum australiense (Calycanthaceae), an arborescent basal angiosperm of Australia's tropical rain forests

Abstract

Idiospermum australiense (Diels) S.T. Blake, a rainforest canopy tree restricted to a few small populations in northeast Australia, is the only southern hemisphere representative of the Calycanthaceae. Pollination processes in Idiospermum were investigated. Flowers are protogynous, with some populations of the species being andromonoecious, whilst others are hermaphrodite. Over their 10 – 16 day floral lifespan, movements of floral organs enforced spatial and temporal separation of male and female floral function. Changes in colour and intensity of fragrance may also influence their attractiveness to potential pollinators. Pollen is present in large quantities, and appears to act as a reward for floral visitors. Insect trapping was carried out both within flowers, and immediately adjacent to inflorescences. A wide variety of arthropods was trapped, with thrips being the most abundant. Other arthropods were trapped, including fourteen species of beetle. For arthropods other than thrips, the mean numbers of adults trapped on flowers remained more or less constant throughout the floral lifetime. However, there was a significant interaction between floral age and the number of pre-adult arthropods present – as the flower aged, the mean number of larvae and eggs per flower increased. The flowers appear to act as sheltered mating and brooding sites for small insects.