The type specimen was collected at a road cutting in Las Mercedes [es] (Tenerife) at an elevation of 850 m (2,790 ft).

The specific epithet honours Canarian botanist Arnaldo Santos of the Botanical Garden of Puerto de la Cruz in Tenerife.

[1] The thallus of Lepraria santosii ranges in form from crustose (crust-like) to somewhat squamulose (scaly) to leprose (powdery or granular).

The granules comprising the thallus are round and 20–100 μm in diameter; they are surrounded by colourless, branching, projecting hyphae.

The photobiont partner is a single-celled green alga whose cells measure about 10–16 μm in diameter and sometimes clump together.