Abstract
Phylogenetic analyses of a combined DNA data matrix containing nuclear small and large subunits (nSSU, nLSU) and mitochondrial small subunit (mtSSU) ribosomal RNA and the largest and second largest subunits of the RNA polymerase II (rpb1, rpb2) of representative Pezizomycotina revealed that the enigmatic genera Xylobotryum and Cirrosporium form an isolated, highly supported phylogenetic lineage within Leotiomyceta. Acknowledging their morphological and phylogenetic distinctness, we describe the new class Xylobotryomycetes, containing the new order Xylobotryales with the two new families Xylobotryaceae and Cirrosporiaceae. The two currently accepted species of Xylobotryum, X. andinum and X. portentosum, are described and illustrated by light and scanning electron microscopy. The generic type species X. andinum is epitypified with a recent collection for which a culture and sequence data are available. Acknowledging the phylogenetic distinctness of Candelariomycetidae from Lecanoromycetes revealed in previous and the current phylogenetic analyses, the new class Candelariomycetes is proposed.