Culture-based study of endophytes associated with rubber trees in Peru reveals a new class of Pezizomycotina: Xylonomycetes

Through a culture-based survey of living sapwood and leaves of rubber trees (Hevea spp.) in remote forests of Peru, we discovered a new major lineage of Ascomycota, equivalent to a class rank. Multilocus phylogenetic analyses reveal that this new lineage originated during the radiation of the 'Leotiomyceta', which resulted not only in the evolution of the Arthoniomycetes, Dothideomycetes, Eurotiomycetes, Geoglossomycetes, Lecanoromycetes, Leotiomycetes, Lichinomycetes, and Sordariomycetes, but also of the majority of hyperdiverse foliar endophytes. Because its origin is nested within this major burst of fungal diversification, we could not recover strong support for its phylogenetic relationship within the 'Leotiomyceta'. Congruent with their long phylogenetic history and distinctive preference for growing in sapwood, this new lineage displays unique morphological, physiological, and ecological traits relative to known endophytes and currently described members of the 'Leotiomyceta'. In marked contrast to many foliar endophytes, the strains we isolated fail to degrade cellulose and lignin in vitro. Discovery of the new class, herein named Xylonomycetes and originally mis-identified by ITSrDNA sequencing alone, highlights the importance of inventorying tropical endophytes from unexplored regions, using multilocus data sets to infer the phylogenetic placement of unknown strains, and the need to sample diverse plant tissues using traditional methods to enhance efforts to discover the evolutionary, taxonomic, and functional diversity of symbiotrophic fungi.