Verrucula arnoldaria

Verrucula arnoldaria is a rare species of lichenicolous (lichen-dwelling) lichen in the family Verrucariaceae. It grows parasitically on the thallus of the rock-dwelling, crustose lichen Calogaya arnoldii. The species was formally described as new to science in 2007 by lichenologists Père Navarro-Rosinés and Claude Roux, from specimens collected in Vaucluse, France. It has also been recorded from Italy. The lichen has a thick brownish-grey, areolate thallus that roughly maintains the shape of its underlying host. The thallus is covered with a crystalline pruina. It makes ellipsoid spores that measure up to about 15 μm long. Its host grows on calciferous rocks and calciferous schists.