It is a straggly shrub with simple, thread-like leaves and white to pink, four-petalled flowers that are pale blue on the back.

The four petals are elliptic, white to pink on the upper surface and pale blue with a darker strip below and 5–7 mm (0.20–0.28 in) long.

[2][3] This species was first formally described in 1875 by Ferdinand von Mueller who gave it the name Boronia defoliata in Fragmenta phytographiae Australiae.

[4][5] In a 2013 paper in the journal Taxon, Marco Duretto and others changed the name to Cyanothamnus defoliatus on the basis of cladistic analysis.

[7] Cyanothamnus defoliatus grows in sand, gravel and laterite between Capel and Manjimup in the Jarrah Forest, Mallee, Swan Coastal Plain and Warren biogeographic regions.