New species of associated with Australian terrestrial orchids in the subtribes Megastylidinae and Thelymitrinae.

(Tulasnellaceae) is a genus of fungus that can form mycorrhizal associations with orchids (Orchidaceae). Here we used molecular phylogenetic analyses and morphological characteristics of pure cultures across four different media to support the description of five new species associated with commonly occurring and endangered Australian orchids. associates with with and respectively. The newly described species were primarily delimited by analyses of five loci: nuc rDNA internal transcribed spacer region ITS1-5.8S-ITS2 (ITS), (adenosine triphosphate [ATP] synthase), (glutamate synthase), (ATP helicase), and mt large subunit 16S rDNA (mtLSU). is introduced for some isolates previously identified as , and this latter species is characterized from multilocus sequencing of a new isolate that matches ITS sequences from the ex-type culture. Morphological differences between the new species are slight. has 6-12 nuclei per hyphal compartment which is the first instance of multinucleate rather than binucleate or trinucleate hyphal compartments in . The formal description of these species of will aid in future evolutionary and ecological studies of orchid-fungal interactions.