Scientists at Royal Botanic Gardens Victoria, The Swedish University of Agricultural Sciences, CSIRO Darwin Laboratories and La Trobe University have identified key ecological needs of Caladenia formosa (Elegant Spider-orchid) for the first time, to improve conservation outcomes. 

The species is nationally threatened and critically endangered under the Flora and Fauna Guarantee Act 1988 (Vic) and vulnerable under the Environment Protection Biodiversity and Conservation Act 1999 (Cth). It was once common in the grassy forests and woodlands of western Victoria and eastern South Australia however has declined due to habitat destruction introduced weeds and feral animals. 

Dr Noushka Reiter, Principal Scientist Conservation, at Royal Botanic Gardens Victoria said that this research spanning over eight years highlights the importance of an integrated approach to re-introducing the species. The team identified the pollinator, selected a reintroduction site where the pollinator was present and protected the species from grazing from native and introduced herbivores. The team also monitored the species’ survival and recruitment to understand limiting factors in the species’ survival and intervene through supplementation.  

“We found that Caladenia formosa needs a specific pollinator, Phymatothynnus pigidialis, a thynnine wasp to reproduce. The wasp removes and deposits pollen onto the orchid in exchange for a small amount of sugar. For more successful conservation outcomes, translocation sites where the pollinator is already present should be selected”. 

“Caladenia formosa is also dependent on a mycorrhizal association with the fungus Serendipita australiana, which supports plants from germination through to adulthood, making the reproductive needs of this species highly specific,” she said. 

Plants in this study were grown from seed with their mycorrhiza Serendipita australiana at Royal Botanic Gardens Victoria. 

“We also found an increased survival rate where the population was fenced off to protect it from herbivores.”  

In 2017, 179 individuals were translocated to both a fenced site and their survival and recruitment were compared to a nearby natural site in the Wimmera. Monitoring over eight years, allowed us to understand the dormancy levels of the species, recruitment and numbers of individuals required to reach a self-sustaining population. 83 adult plants of reproductive age were added in 2024, which resulted in nearly a 3-fold increase in the number of fruits produced relative to previous years. The long-term aim will be to bring the site numbers up to around 500 plants. 

“This research makes a significant step in improving conservation outcomes for this species to bring it back from the brink of extinction,” said Dr Reiter. 

The Caladenia genus is the most threatened orchid genus in Australia, with 73 species at risk of extinction. 

Australia is home to over 1,700 of the world’s orchid species, many of which are terrestrial (ground dwelling) rather than tree dwelling. Around 90% are found nowhere else on Earth.