Royal Botanic Gardens Victoria has marked a major milestone in the conservation of one of Australia's rarest orchids, with 500 critically endangered rosella spider orchids (Caladenia rosella) planted into a protected Victorian site as part of a long-term recovery program.

The planting almost doubles the number of rosella spider orchids growing in the wild and establishes a fifth population for the species, which is found only in Victoria and is listed as critically endangered.

The orchids were propagated from seed by Royal Botanic Gardens Victoria's Orchid Conservation Program, which specialises in cultivating threatened native orchids for reintroduction into the wild. The process takes several years and relies on cultivating the specific fungal partners orchids need to germinate and grow.

Royal Botanic Gardens Victoria Research Scientist Alex McLachlan said the planting represented years of work by scientists, volunteers and conservation partners.

"We're incredibly excited to see these orchids returned to the wild where they belong. Growing threatened orchids from seed is a complex process, and every plant represents years of dedicated conservation effort."

The rosella spider orchid once occurred more widely across Victoria but is now restricted to just a handful of locations north-east of Melbourne. While only around 120 wild plants remained in 2000, ongoing habitat protection and recovery efforts have helped increase numbers to more than 650 mature plants.

The planting forms part of Royal Botanic Gardens Victoria's broader conservation work, with approximately 500 orchid species currently in propagation and multiple threatened plant species scheduled for reintroduction programs this year.

Working alongside Trust for Nature, university researchers, orchid societies and community volunteers, Royal Botanic Gardens Victoria is helping safeguard Victoria's unique orchid diversity and prevent threatened species from disappearing forever