Seven new Serendipita species associated with Australian terrestrial orchids

Serendipita is one of the main fungal genera that form mutualistic associations with species of orchids (Orchidaceae). Here, seven new Serendipita species associated with various Australian orchid genera are described. These Serendipita species were originally characterized by multilocus DNA sequence species delimitation analyses (three mtDNA and four nuclear genes) and confirmed as distinct with addition of further isolates and reanalysis of nuc rDNA internal transcribed spacer region ITS1-5.8S-ITS2 (ITS) and nuc 28S rDNA (28S). Culture morphology and microscopic features are presented for each species, three of which are binucleate and four multinucleate. For the ITS region, the seven species have within-species sequence divergence between 1.07% and 4.31%, and all but one of the species pairs is separated by interspecific divergence of at least 4.35%. The newly described Serendipita species, S. australiana, S. communis, S. occidentalis, S. rarihospitum, S. secunda, S. talbotii, and S. warcupii, are shown to be separate species from S. vermifera on the basis of comparison against a sequence from the type. Isolates originally identified by Warcup as Sebacina “vermifera” from Caladenia orchids are revised and shown to belong to three of the species newly described here. Some non-Caladenia isolates identified by Warcup as S. “vermifera” are also shown to be non-conspecific with the type of S. vermifera. On the basis of ITS sequences, 346 isolates from 26 other studies, previously identified under provisional designations, are accommodated under the novel species. The species of Serendipta described here associate with the Australian orchid genera Caladenia, Cyanicula, Elythranthera, Ericksonella, Eriochilus, Glossodia, and Pheladenia. Most of the novel Serendipita species occur widely across Australia, often with widely distributed hosts, but one species, Serendipita rarihospitum, associates with narrowly distributed orchid species.