Ocellularia diospyri is a rare species of corticolous (bark-dwelling) lichen in the family Graphidaceae.

The lichen was formally described as a new species in 2002 by lichenologists Natsurang Homchantara and Brian J. Coppins.

The type specimen was collected from Ton Krabak Yai National Park (Tak Province) at an elevation of about 500 m (1,600 ft); here, in a mixed forest, it was found growing on the trunk of a Diospyros tree.

The columella (the sterile central axis of the apothecia) is carbonized (blackened) and is visible from the small apothecial pore; it measures 0.08–0.2 mm in diameter.

The ascospores are thin walled, spindle-shaped, and have from 12 to 23 locules (cavities); they typically measure 102.5–164.5 by 15.0–20.5 μm.