Five new species in the Tremella caloplacae complex

Abstract Tremella caloplacae (Zahlbr.) Diederich is a species complex including at least nine different species. Here, we formally describe the new species Tremella elegantis , T. nimisiana , T. parietinae , T. pusillae and T. sorediatae . Tremella elegantis induces galls in the hymenium of Rusavskia elegans and forms 2-celled basidia, where cells rarely elongate and sometimes give the appearance of two immature, independent basidia. Tremella nimisiana has small basidiomata (less than 1 mm diam.), narrowly ellipsoid to pyriform 2-celled, occasionally clavate to subcylindrical 3-celled basidia, and grows in the hymenium of Xanthocarpia species. Tremella parietinae is characterized by the exclusive growth in the hymenium of Xanthoria parietina , the broadly fusiform to ellipsoid probasidia, and the subspherical, pyriform or ellipsoid 2(–3)-celled basidia. Tremella pusillae has ellipsoidal probasidia, 2(–3)-celled pyriform or ellipsoidal basidia that sometimes are constricted at the septum, and grows only on Calogaya pusilla . Tremella sorediatae is characterized by inducing galls on the thallus of Rusavskia sorediata and by pyriform to ellipsoid basidia that sometimes are constricted at the septum. Three species are not formally described and are left unnamed as Tremella sp. 13 on Calogaya biatorina , Tremella sp. 14 on Calogaya decipiens and Tremella sp. 15 on Polycauliona sp. Tremella caloplacae in the strict sense is re-circumscribed as a species confined to Variospora species.