[1] The genus contains a single species, Tenuitholiascus porinoides, a foliicolous (leaf-dwelling) lichen found in China.

The genus name, which refers to its characteristic thin-walled asci, is derived from Latin roots: tenuis- ("slender"), tholus ("dome"), and ascus ("tube" or "bag").

[2] Molecular phylogenetic analysis revealed that the fungus represented a previously unknown lineage in the Dothideomycetes, forming a clade with a sister group relationship to the Strigulaceae, a family mostly comprising foliicolous lichen-forming fungi.

[2] The lichen, which lives on the cuticle of the leaf (and is readily removed from its surface), is smooth and pale green, measuring 3–12 mm in diameter and about 30–50 μm thick.

Tenuitholiascus porinoides produces colourless,fusiform spores that have 3 septa and measure 25–30 by 6–8 μm.