Hidden in the tropics: Retiperidiolia gen. nov., a new genus of bird’s nest fungi ( Nidulariaceae ), and a systematic study of the genus Mycocalia

Nidulariaceae (bird’s nest fungi) are an understudied group of fungi, and species of Mycocalia J.T. Palmer are the least known taxa in the family. Mycocalia was previously shown to be polyphyletic, but no further research has been conducted to revise the taxonomy of the genus. Here we conduct a phylogenetic study of Mycocalia species using five loci (ITS, LSU, SSU, TEF1 , and RPB2 ) and morphologically examined Mycocalia collections available in herbaria. Our results indicate that two tropical Mycocalia species, M. aquaphila and M. reticulata , are distantly related to M. denudata , the type species of this genus. Accordingly, we propose the new genus Retiperidiolia to accommodate this phylogenetically and morphologically unique bird’s nest fungus lineage, with R. reticulata as the type species. Retiperidiolia reticulata was originally described from Sri Lanka by Petch in 1919. Because the type specimen is in poor condition and no molecular data can be obtained, we designated an epitype based on a recent collection from Thailand. Species of Retiperidiolia closely resemble Mycocalia species except that the peridiole cortex in Retiperidiolia species has a reticulated pattern and members of this lineage are thus far known only from tropical or subtropical habitats. In addition to phylogenetic and morphological characterization, we revised the taxonomy and provided a revised key to accepted species of Mycocalia and Retiperidiolia .