Exidia is a genus of fungi in the family Auriculariaceae. The species are saprotrophic, occurring in attached or recently fallen dead wood, and produce gelatinous basidiocarps (fruit bodies). The fruit bodies are diverse: pustular, lobed, button-shaped, cup-shaped, or effused. Several species, including the type species Exidia glandulosa, have sterile pegs or pimples on their spore-bearing surface. The genus has a cosmopolitan distribution and over 25 species are currently recognized worldwide.
Taxonomy Exidia species were originally placed in the genus Tremella along with many other gelatinous fungi. The genus Exidia was separated from Tremella by Fries in 1822, based mainly on fruit body shape. Fries initially included species now assigned to Auricularia within the genus.
Tremellochaete was originally created in 1964 by Estonian mycologist Ain Raitviir to accommodate Tremellochaete japonica, a species with a notably spiny hymenium that appeared morphologically intermediate between Exidia and Heterochaete. The genus was initially thought to be distinct as a result of molecular research, based on cladistic analysis of DNA sequences. But subsequent research has reduced it to synonymy with Exidia.
Molecular research has indicated that Exidia as formerly circumscribed was an artificial grouping. Accordingly, some species previously placed in Exidia have now been transferred to the genera Descidia and Ulocolla, leaving Exidia sensu stricto as a natural grouping. A number of species have, however, yet to be sequenced.
Description Exidia fruit bodies are gelatinous, most non-effused species having a distinct spore-bearing upper surface and a sterile undersurface. These surfaces are either smooth or (in some species) covered in dense or scattered sterile pegs or pimples. Fruit bodies grow either separately or in groups, in which case they may coalesce.
Microscopic characters Exidia fruit bodies are composed of hyphae with clamp connections in a gelatinous matrix. The spore-bearing surface is initially covered in a layer of branched hyphidia below which the basidia are formed. The basidia are tremelloid (ellipsoid and vertically septate), giving rise to long, sinuous sterigmata or epibasidia on which the basidiospores are produced. These spores are allantoid (sausage-shaped) or less commonly oblong to cylindrical.
Species The list below comprises species of Exidia (including those now referred to Descidia and Ulocolla) that have recently been described or redescribed. Species marked with an asterisk have been sequenced and belong to Exidia sensu stricto. Some additional older species may also be valid, but lack a modern description. The type locality (but not the wider distribution) is given for each species.
Image Name Type Locality Exidia aeruginosa Jamaica Exidia alveolata Ecuador Exidia ambipapillata Guatemala Exidia antiguae Guatemala Exidia brunneola Finland Exidia candida* USA Exidia ciliata* Brazil Exidia compacta USA Exidia crenata* USA Exidia cystidiata USA Exidia delita* France Exidia friesiana* Finland Exidia glandulosa* France Exidia impressa* France Exidia inornata* France Exidia japonica* Japan Exidia lutea Guatemala Exidia maracensis Brazil Exidia maya Guatemala Exidia mexicana Mexico Exidia nothofagi New Zealand Exidia panamensis Panama Exidia pergamena Brazil Ulocolla pinicola USA Exidia pithya* Sweden Exidia plumbescens* USA Exidia purpureocinerea South Africa Exidia pusilla Brunei Exidia recisa* Germany Exidia reflexa China Descidia repanda Sweden Ulocolla saccharina Sweden Exidia repleta* France Exidia saturata* France Exidia semiorbis* Russia Exidia spiculata* USA Exidia straminea* France Exidia subglandulosa* China Exidia tanzanica* Tanzania Descidia thuretiana France Exidia truncata* Sweden Exidia tucumanensis Argentina Exidia umbrinella* Italy Exidia uvapassa* Japan Exidia yadongensis* China Exidia zelleri* USA
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