Multigene phylogeny of , an early diverging lineage of fungi associated with plants.

is a lineage of early diverging fungi within . Many species in this order produce small sporophores ("sporocarps") containing a large number of zygospores, and many species form symbioses with plants. However, due to limited collections, subtle morphological differentiation, difficulties in growing these organisms , and idiosyncrasies in their rDNA that make PCR amplification difficult, the systematics and character evolution of these fungi have been challenging to resolve. To overcome these challenges we generated a multigene phylogeny of using sporophores collected over the past three decades from four continents. Our results show that harbour significant undescribed diversity and form two deeply divergent and well-supported phylogenetic clades, which we delimit as the families and fam. nov. The family consists of the genus , and many diverse lineages known only from environmental DNA sequences of plant-endosymbiotic fungi. Within there are two clades. One corresponds to and includes the type species, . Species of are characterized by above- and below-ground sporophores, a hollow and infolded sporophore form, a loose zygosporangial hyphal mantle, homogeneous gametangia, and an enigmatic trophic mode with no evidence of ectomycorrhizal association for most species. For the other clade we introduce a new generic name, gen. nov. Members of that genus ( and species complexes, and an undescribed species) are characterized by hypogeous sporophores with a solid gleba, a well-developed zygosporangial hyphal mantle, heterogeneous gametangia, and an ectomycorrhizal trophic mode. Future studies on and will be important for understanding fungal innovations including evolution of macroscopic sporophores and symbioses with plants.