extrema is a terrestrial, perennial, deciduous, herb with an underground tuber and which usually grows as solitary plants.

The lateral sepals and petals are linear to lance-shaped in the lower quarter of their length, then suddenly taper to downcurved, narrow ends.

[1][2][3] Caladenia longicauda was first formally described by John Lindley in 1840 and the description was published in A Sketch of the Vegetation of the Swan River Colony.

[3] The late white spider orchid is only known from a small area near Manjimup in the Jarrah Forest biogeographic region where the type specimen was collected.

extrema is classified as "Priority One" by the Western Australian Government Department of Parks and Wildlife,[7] meaning that it is known from only one or a few locations which are potentially at risk.