Cyanothamnus tenuis, commonly known as blue boronia,[2] is a species of plant in the citrus family, Rutaceae, and is endemic to the southwest of Western Australia.

It is a slender shrub with thread-like, sessile leaves, and flowers with four petals that are white to pink on the front and pale blue on the back.

[2][3] Cyanothamnus tenuis was first formally described in 1839 by John Lindley in A Sketch of the Vegetation of the Swan River Colony.

It is found on the Darling Scarp between Dwellingup and Wannamal in the Jarrah Forest and Swan Coastal Plain biogeographic regions.

[3][2] Cyanothamnus tenuis is classed as is classified as "Priority Four" by the Government of Western Australia Department of Parks and Wildlife,[2] meaning that is rare or near threatened.