Verrucaria viridula is a common and widely distributed species of saxicolous (rock-dwelling), crustose lichen in the family Verrucariaceae.

[2][3] Verrucaria viridula presents a thallus — the main body of the lichen — that is partially to entirely immersed in the cracks of its rocky substrate, sometimes only discernible as brown flecks on the surface.

Pycnidia, another type of fruiting body, are identifiable as dark dots up to 0.06 mm wide or larger.

[7] Opegrapha opaca is a lichenicolous (lichen-dwelling) fungus that inhabits the thallus of V. viridula, although it causes little to no discernible damage to its host.

This genus-specific fungus (it has been found on other Verrucaria species as well) has been recorded from western Europe east to Israel.