Catillaria gilbertii is a rare species of saxicolous (rock-dwelling), crustose lichen in the family Catillariaceae.

The type specimen was collected by the first author from the Ben Lawers National Nature Reserve (Perthshire) at an altitude of 890 m (2,920 ft); there, it was found growing on an east-facing mica-schist rock face.

[2] They noted that the naming of this species, which produces twice the usual number of ascospores in its asci, was "particularly appropriate given the pre-disposition of the Gilbert family for producing twice the usual number of offspring at a time; Dr Gilbert himself is a twin and he also has twin daughters".

Its ascospores are hyaline with an oblong to ellipsoid shape and a single septum, and measure 10–12 by 2.5–3 μm.

[2] It is one of relatively few endemic lichens known in Scotland, and one of even fewer that inhabit the hyper-oceanic mountain habitat, above the tree line.