Caladenia rhomboidiformis, commonly known as the diamond spider orchid, is a species of orchid endemic to the south-west of Western Australia. It has a single erect, hairy leaf and one or two green, yellow and red flowers. Until 1971 It was known as a variety of the green comb spider orchid Caladenia dilatata then, until 1989 as a variety of the clubbed spider orchid, Caladenia longiclavata.
Caladenia rhomboidiformis is a terrestrial, perennial, deciduous, herb with an underground tuber and a single erect, hairy leaf, NaNsigfig=1NaNsigfig=1 long and about 2sigfig=1NaNsigfig=1 wide. One or two green, yellow and red flowers NaNsigfig=1NaNsigfig=1 long, NaNsigfig=2NaNsigfig=2 wide are borne on a stalk NaNsigfig=1NaNsigfig=1 tall. The sepals have yellowish to brown, club-like glandular tips NaNsigfig=1NaNsigfig=1 long. The dorsal sepal is erect, NaNsigfig=1NaNsigfig=1 long and NaNsigfig=1NaNsigfig=1 wide. The lateral sepals are NaNsigfig=1NaNsigfig=1 long, NaNsigfig=1NaNsigfig=1 wide, turn stiffly downwards and roughly parallel to each other. The petals are NaNsigfig=1NaNsigfig=1 long, NaNsigfig=1NaNsigfig=1 wide, spread widely and are also turned stiffly downwards. The labellum is NaNsigfig=2NaNsigfig=2 long, NaNsigfig=2NaNsigfig=2 wide, broadly diamond-shaped and white to yellow with a deep red tip. The sides of the labellum have greenish teeth up to 2sigfig=1NaNsigfig=1 long and the tip is curled under. There are four rows of deep red calli along the mid-line of the labellum. Flowering occurs from September to October.[1] [2] [3]
This orchid was first described in 1930 by Edith Coleman who gave it the name Caladenia dilatata var. rhomboidiformis and published the description in The Victorian Naturalist.[4] [5] In 1971, Alex George recognised it as Caladenia longiclavata var. rhomboidiformis[6] and in 1989 Mark Clements and Stephen Hopper raised it to species status.[7] The specific epithet (rhomboidiformis) is derived from the Ancient Greek word ῥόμβος rhombos meaning "rhombus",[8] the suffix oid meaning "likeness" and the Latin word forma meaning "shape" or "figure" referring to the diamond-shaped labellum of this orchid.
The diamond spider orchid is found between Busselton and Augusta in the Jarrah Forest and Warren biogeographic regions where it grows in a variety of habitats but often in jarrah forest, or Banksia or sheoak woodland.
Caladenia rhomboidiformis is classified as "not threatened" by the Western Australian Government Department of Parks and Wildlife.