Caladenia robinsonii

Caladenia robinsonii, commonly known as the Frankston spider orchid is a rare species of orchid which is endemic to Victoria, Australia. A shoot arises from the tuber each year in the early autumn producing a solitary leaf in May. In September to October a single (or rarely two) red and creamy yellow flower is produced on a hairy stem up to 30 cm high The flower is up to 4cm in width and has narrow sepals, four of which spread out horizontally plus an erect dorsal sepal.^[2]

The flowers exude a scent that mimics pheromones of the female Thynnid wasp, which attracts male wasps that pollinate the flowers.^[3] The orchid has a symbiotic relationship with a mycorrhizal fungus that enables it to absorb nutrients.^[3]

It occurs in Coast Manna Gum woodland, on the Mornington Peninsula and was first formally described by G.W. Carr in 1991 from material collected in Frankston North.^[1] This population was lost when the locality was developed in the 1990s for housing. However a second population was discovered at Rosebud in 1990.^[3] Potential threats to the latter population, estimated to be around 40 plants, include weed invasion, tramping, fire and grazing by rabbits.^[2] In 2010, 150 of the orchids were planted in rehabilitated areas by volunteers, utilising seed that had been propagated by the Royal Botanic Gardens.^[4]

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