Wet Tropics a critical refuge for Australia’s Rock Orchid

The genetic study of Australian Rock Orchids by PhD candidate Lalita Simpson was co-authored with her supervisors, Darren Crayn and Katharina Nargar at the Australian Tropical Herbarium, and Mark Clements at the Australian National Herbarium and has been published in the journal Molecular Phylogenetics and Evolution.

Ms Simpson said evidence from the genetic analysis had shown the orchid Dendrobium speciosum, which only occurs in Australia and previously had been thought to consist of up to 11 species, was in fact a single species with two subspecies, one northern and one southern.

“The study reconstructed the distribution of the Rock Orchid under past climatic conditions, which showed a large barrier of unsuitable habitat between Rockhampton and Mackay separated the northern and southern populations in the past,” she said.

“This prevented the exchange of pollen and seeds and as a result two subspecies have evolved.

“We modelled the distribution of the Rock Orchid under different climate scenarios predicted for the future and found the northern subspecies which grows between Cooktown and Mackay will be the most severely impacted by climate change.

“With average global temperatures warming beyond a two degree increase we found that by 2080, those wanting to see the Rock Orchid’s spectacular flowers in Queensland’s bush would only be able to do so in the Wet Tropics.

“However, if warming was contained below a two degree increase, suitable habitat would be maintained in several regions along Queensland’s east coast.

“The southern subspecies, which occurs between Rockhampton and the New South Wales and Victorian border, is not as greatly affected as its relatives in the north, although lowland populations along the coast are also threatened.”

Australian Tropical Herbarium Director Professor Darren Crayn said the study showed how important climate change was for the evolution of biodiversity, both creating and extinguishing it.

“Ancient climate change drove the evolution of the two subspecies of Rock Orchids from their common ancestor, and now it looks like future climate change will reduce one of them to a small fraction of its current distribution,” he said.

Dr Mark Clements said samples were collected from across the entire species range along the east coast of Australia and took more than 30 years to accumulate.

“The results resolve recent controversies regarding the best classification for this grand orchid which is one of Australia’s truly iconic and recognisable indigenous orchids.”

The Australian Tropical Herbarium is a joint venture between CSIRO, Australian and Queensland Governments and James Cook University. The Australian National Herbarium is part of the Centre for Australian National Biodiversity Research, a joint venture between Parks Australia’s Australian National Botanic Gardens and CSIRO.

Images available here.