A new species of Phyllopsora (Lecanorales, lichen-forming Ascomycota) from Dominican amber, with remarks on the fossil history of lichens.

Phyllopsora dominicanus sp. nov. (Bacidiaceae, Lecanorales, lichen-forming Ascomycota) is described and illustrated from Dominican amber. The diagnostic features of the lichen include a minute subfolious thallus of lacinulate, ascending squamules, a well-developed upper cortex, and a net-like pseudocortex on the lower surface. The algal symbionts are unicellular green algae, forming a distinct layer immediately below the upper cortex. The fossil demonstrates that distinguishing features of Phyllopsora have remained unchanged for tens of millions of years. The fossil also provides the first detailed views of mycobiont-photobiont contacts in Tertiary green algal lichens. The mycobiont hyphae formed apical and intercalary appressoria by pressing closely against the photobiont cells. This indicates that a conserved maintenance of structure is also seen in the fine details of the fungal-algal interface.