Lepraria crassissima is a species of leprose lichen in the family Stereocaulaceae.

The species was first described as Crocynia crassissima by Auguste-Marie Hue in 1924,[3] and was later transferred to Lepraria by Georg Lettau in 1958.

Older specimens often show eroded patches where the medulla is exposed.

The reproductive structures consist of abundant coarse granules (soredia) up to 300–400 micrometres in diameter, with projecting threads (hyphae) that can be short to long.

Well-developed specimens may develop large granules or warts that somewhat resemble isidia but lack a cortex, and these may become sorediate.