The new genus of epiphyllous fungi on sequoioid leaves from the Albian-Cenomanian of Western Siberia, Russia.

Co-evolution of plants and fungi is of great importance for the phylogeny of both groups. Here we establish fossil thyriothecioid stromata on sequoioid (Cupressaceae) leaves from the Albian-Cenomanian of Western Siberia, Russia, which are assigned to the new fossil genus and species, Kiyamyces sequoiae. The new genus is described on the basis of thyriothecioid stromata arising from a host plant stoma, appearing first as a columella and with tendency to be confluent forming crusts. Thyriothecioid stromata are characterized by a "basal layer," a scutellum of radial, septate cells, a pseudoparenchyma inside the thyriothecioid stromata; a prominent hypostroma and an endophytic, septate mycelium. The new data contribute to our understanding of the range of character combinations of early epiphyllous Ascomycota. The newly discovered fungus and the conifer plant in the Cretaceous extend the range of character combinations of early epiphyllous Dothideomycetes.