Varicellaria hemisphaerica is a species of crustose lichen belonging to the family Varicellariaceae.[1] It has an almost cosmopolitan distribution.
Varicellaria hemisphaerica can be distinguished from the closely related V. lactea by its preference and morphological features: V. hemisphaerica grows exclusively on tree bark (corticolous), while V. lactea is found on rock surfaces (saxicolous). The species produces smaller soredia (40–100 μm in diameter) compared to V. lactea (110–180 μm). While both species contain lecanoric acid as their main secondary metabolite, the presence of variolaric acid can occur in both species and is not a reliable diagnostic feature. The thallus of V. hemisphaerica is typically pale bluish-grey, sometimes becoming pink in herbarium specimens, with a smooth and thin or cracked and thick texture, featuring convex soralia that are paler or the same colour as the thallus. Molecular phylogenetic studies have confirmed that V. hemisphaerica and V. lactea represent distinct species, with their divergence likely driven by their different substrate requirements. Both species associate with the same, Trebouxia sp. OTU A03.