Fungi in the Nidulariaceae, otherwise known as ‘bird’s nest fungi’, are among the least studied groups of Agaricomycetes (Basidiomycota). Bird’s nest fungi are globally distributed and typically grow on woody debris or animal dung as saprotrophs. This group of fungi is morphologically diverse, and ca. 180 different species have been described. Phylogenetic relationships of bird’s nest fungi were investigated with Maximum Likelihood and Bayesian analyses of four commonly used loci (ITS, LSU, tef, and rpb2). The family was resolved as a monophyletic group with Psathyrellaceae and Squamanitaceae as potential sister taxa. Specimens identified as Cyathus and Crucibulum formed well-supported clades. Nidula and Nidularia together are monophyletic. Two Mycocalia species studied are on their own separate branches. Misidentifications were detected in most genera. Common bird’s nest fungi species have global geographical distributions whereas rarer species may have more limited ranges. Our data also indicate that basic morphological characters of bird’s nest fungi have likely been lost or gained multiple times. The relationships among genera of bird’s nest fungi remain largely unresolved and the sister lineage of bird’s nest fungi is still unclear. Further studies with data from rare species and additional informative loci are needed to resolve the topology of this family and to identify a sister group with more certainty. We also provide a detailed morphological comparison to differentiate the five currently accepted genera of Nidulariaceae.

Specimens of Nidulariaceae fungi were obtained through three different methods: fresh field collections, contributions from citizen scientists and traditional herbarium loans.