Caeruleum is a genus of lichen-forming fungi in the family Acarosporaceae.

Caeruleum is generally similar to the related genus Acarospora.

[1][2] The generic name, "Caeruleum", refers to the blue color stain of the tholus after treatment with Lugol's iodine.

Arcadia & Knudsen (2012) noted that future research may indicate that C. immersum represents a synonym of C.

[1] Caeruleum is one of eleven genera within the Acarosporaceae family of fungi.