Botanic Gardens Trust, Sydney, Australia

Orchids

DNA of Ground Orchids

Peter Weston, Botanist

Orchids tend to have kinky sex lives, and in this respect Australian native ground orchids out-do all others. Many of them attract male pollinating insects by convincingly mimicking the corresponding females. The flowers exude appropriate pheromones, the powerful chemical signals with which female insects attract males over considerable distances. The male insect mounts the flower and attempts to mate with it but pollinates it instead.

Scientists at the Royal Botanic Gardens & Domain Trust are investigating the evolution of ‘pseudocopulation’ in some groups of Australian ground orchids by reconstructing the evolutionary history of the orchids and their wasps using information from DNA sequences. So far we have been able to show that pseudocopulation has evolved independently in at least seven different lineages of orchids. We have also made a detailed study of the relationship between the orchid genus Chiloglottis and its male wasp pollinators. This work has shown that the orchids are a younger group than their wasps. The ancestor of these orchids appears to have fortuitously ‘stumbled’ on a pheromone that attracted males of a particular wasp species. Its descendants then diversified by gradually ‘colonising’ close relatives of this ‘first wasp’.

Orchids are one of the largest and most diverse families of flowering plants, including somewhere between 20 000 and 35 000 species, which together occupy almost every ecological niche on land. Some grow to the size of a small truck, while others are moss-like plants that would happily grow in a thimble. The flowers of some are huge and flamboyant while others are no larger than a pinhead. Many orchids live in soil like ‘normal’ plants but most species are epiphytes - plants that perch on, or hang suspended from, the trunks, branches and twigs of trees. More than 800 orchid species are native to Australia, where they grow in lowland tropical rainforests to alpine meadows, from coastal sand dunes to the semi-arid regions of the continent.

Peter-Weston

native orchid

Extracting pollen