Systematics, diversification, and functional diversity of Russulaceae (Russulales)

The family Russulaceae is an iconic family of mushroom-forming Basidiomycetes both because of their importance as edible mushrooms in many parts of the world and their species richness in both temperate and tropical forested biomes. While much mycological research has been focused on this group, recent systematic and ecological research has failed to develop a comprehensive or cohesive organization by which to understand the evolutionary relationships, patterns of diversification, or functional importance of the group. Recently, interest in ectomycorrhizal fungi (EmF), of which Russulaceae is a key lineage, has greatly increased due to the recognition of the importance of EmF in carbon sequestration in the face of global climate change. By specifically taking a lineage-based approach to the study of Russulaceae, this work is an attempt to elucidate the biological importance of this group as a model for understanding important biological patterns in EmF. To this end, this dissertation work seeks to address five key questions: 1) What are the major systematic relationships in the Russula, Russulaceae, and their placement within Russulales? 2) What are the biogeographic and host patterns in Russula? 3) What factors have contributed to the high diversification of Russula? 4) What are the functional differences between major groups within Russulaceae? 5) To what extent have members of Russulaceae retained the ability to decompose soil organic matter?

To address these main questions, my research has combined the collection and study of sporocarps with molecular phylogenetics and contemporary evolutionary analytics. These efforts have led to the first multi-gene phylogeny of the genus Russula with a clade-based classification system proposed. By applying ancestral area reconstruction methodologies and diversification analyses using state speciation-extinction (SSE) models, I have inferred a temperate origin associated with angiosperms for Russula. I have provided support for a higher net diversification rate in temperate species of Russula that is not a result of migration. Here I present a molecular systematic revision of the Roseinae clade and provide support for at least 5 new species. Finally, in a comparative genomic analysis I show that Russulaceae are widely diverse in gene content, indicating diverse functional roles.