Rhizocarpon timdalii is a species of saxicolous (rock-dwelling), crustose lichen in the family Rhizocarpaceae.

The type specimen of Rhizocarpon timdalii was collected near Sawbill Lake in Cook County, Minnesota, USA.

This collection was made in a mixed conifer-hardwood forest near a lake, suggesting a preference for acidic rock habitats.

[2] The species epithet honours Einar Timdal of the University of Oslo for his contributions to the taxonomy of the genus Rhizocarpon.

The exciple is coloured dark blue-green and reacts negatively to standard lichen spot tests.