Pertusaria medullamarilla is a species of saxicolous (rock-dwelling), crustose lichen in the family Pertusariaceae.

[1] Found on the Galápagos Islands, it was formally described as a new species in 2015 by lichenologists Alba Yánez-Ayabaca, Frank Bungartz, Alan W. Archer, and John Elix.

The type specimen was collected on Pinzón Island, where it was found growing on basalt.

The species epithet refers to its yellow-coloured medulla (amarilla is Spanish for yellow).

This Pertusariales-related article is a stub.