mycological research 111 (2007) 1040–1063 journal homepage: www.elsevier.com/locate/mycres Re-thinking the classification of corticioid fungi Karl-Henrik LARSSON Go¨teborg University, Department of Plant and Environmental Sciences, Box 461, SE 405 30 Go¨teborg, Sweden article info abstract Article history: Corticioid fungi are basidiomycetes with effused basidiomata, a smooth, merulioid or Received 30 November 2005 hydnoid hymenophore, and holobasidia. These fungi used to be classified as a single Received in revised form family, Corticiaceae, but molecular phylogenetic analyses have shown that corticioid fungi 29 June 2007 are distributed among all major clades within Agaricomycetes. There is a relative consensus Accepted 7 August 2007 concerning the higher order classification of basidiomycetes down to order. This paper Published online 16 August 2007 presents a phylogenetic classification for corticioid fungi at the family level. Fifty putative Corresponding Editor: families were identified from published phylogenies and preliminary analyses of unpub- Scott LaGreca lished sequence data. A dataset with 178 terminal taxa was compiled and subjected to phy- logenetic analyses using MP and Bayesian inference. From the analyses, 41 strongly Keywords: supported and three unsupported clades were identified. These clades are treated as fam- Agaricomycetes ilies in a Linnean hierarchical classification and each family is briefly described. Three ad- Basidiomycota ditional families not covered by the phylogenetic analyses are also included in the Molecular systematics classification. All accepted corticioid genera are either referred to one of the families or Phylogeny listed as incertae sedis. Taxonomy ª 2007 The British Mycological Society. Published by Elsevier Ltd. All rights reserved. Introduction develop a downward-facing basidioma. Dead wood on the ground serves that purpose well and such species were earlier Corticioid fungi are homobasidiomycetes with effused, resu- falsely designated as wood-decaying. pinate fruiting structures that usually develop on the under- The name corticioid means ‘resembling a [member of the side of decaying wood. As they are effused they do not have genus] Corticium’, the type genus for the family Corticiaceae. a definite form and extend over the substrate until they are Donk (1964) tried to create well-defined families for homoba- checked by competition or unsuitable growth conditions. Re- sidiomycetes without gills (Aphyllophorales). His paper was supinate means that basidiomata are fully attached to the an important step towards a natural classification for fungi, substrate and not revolved or reflexed at the margin. None but he admittedly failed to find a reliable system for the of these definitions are absolute as some corticioid fungi corticioid fungi. Still the family name Corticiaceae has found form a disc-like basidioma instead of being effused (for exam- wide application as a convenient label for an assemblage of ple Aleurodiscus amorphous) and some species have developed morphologically similar fungi much in the same way as more or less erect fruiting structures (for example Sistotrema Polyporaceae has been used for all polypores. confluens). A change of term from Corticiaceae to ‘corticioid fungi’ The connection to dead wood has two explanations. Most reflects the radically increased knowledge of fungal evolution species are true wood decayers and extend their vegetative gained from molecular phylogenetic analyses (e.g. Larsson mycelium inside the slowly degrading wood resource. Other et al. 2004; Binder et al. 2005). As these analyses now make it species live in soil but need a firm structure upon which to possible to define Corticiaceae in a strict sense, its use as E-mail address: [email protected]. 0953-7562/$ – see front matter ª 2007 The British Mycological Society. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.mycres.2007.08.001 Classification of corticioid fungi 1041 a classification label for all corticioid fungi should be aban- The foundation of contemporary corticiology can be traced doned. The same phylogenetic analyses have also shown back to Bourdot, who, together with his friend and colleague that the term ‘corticioid fungi’ refers to a highly polyphyletic Galzin, published numerous new species and finally summa- group, even more so than anticipated by Donk in 1964. Not rized his knowledge in the monumental Hyme´nomyce`tes de only are they distributed over all currently identified evolu- France (Bourdot & Galzin 1928). This book enabled, for the first tionary lineages among the Agaricomycetes (syn. Homobasidio- time, the identification of corticioid fungi with at least accept- mycetes) but they also blend with nearly all other able accuracy. In fact, no alternative handbooks were avail- morphogroups from the Friesian classification. With such able until the publication of The Corticiaceae of North Europe a ubiquitous presence corticioid fungi emerge as a key group (Eriksson & Ryvarden 1973, 1975, 1976; Eriksson et al. 1978, for understanding homobasidiomycete evolution, and at least 1981, 1984; Hjortstam et al. 1988a,b), although Danish Resupi- some ancestral character state analyses favour a corticioid- nate Fungi (Christiansen 1960) must be mentioned as a remark- like fungus as the ancestor of all homobasidiomycetes (Hib- able achievement. bett & Binder 2002; but see Hibbett 2004). Bourdot & Galzin used the old traditional genera for corti- Early classifications of larger basidiomycetes placed the cioid fungi, e.g. Corticium, Peniophora, and Gloeocystidium, but main emphasis either on basidioma construction or on hyme- sorted species in sections that they perceived as natural groups, nophore configuration, or a combination of both. Persoon thus initiating the splitting of the Friesian genera. The chal- (1801), for example, kept all species with a toothed hymeno- lenge was adopted first and foremost by Donk who, in a series phore in Hydnoidei (Sistotrema, Hydnum, Odontia) and those of influential papers, introduced new genera or emended with a smooth hymenophore in Gymnodermata (Thelephora, long-forgotten, but valid, genus names (Donk 1931, 1956, Stereum, Corticium). The last classification to be published by 1957, 1958). Other important contributions were made by Eriks- Fries (1874) comprised two main groups for the Hymenomy- son (1958), Oberwinkler (1965), and Parmasto (1968). The latter cetes: (1) hymenial surface uneven; (2) hymenial surface publication also introduced a classification for all corticioid even. The former group contained three subgroups based on fungi. Parmasto basically followed Donk (1964) but restricted hymenophore configuration: Agaricini, Polyporei, and Hydnei. Corticiaceae to monomitic species and created Steccherinaceae In the latter group, species were divided according to hyme- for dimitic corticioid species. Each family was further divided nial position in Thelephorei (hymenium horizontal, below), into subfamilies and tribes, and some of the genera were Clavariei (hymenium vertical, amphigenous), and Tremellinei divided into subgenera. Several of the new taxa introduced by (hymenium above, gelatinous). Parmasto have later been raised to family and genus level. Berkeley (1860) divided Hymenomycetes into six ‘orders’, Among the many contemporary mycologists who have among them Hydnei (Hydnum, Sistotrema, Irpex, Radulum, studied the taxonomy of corticioid fungi two in particular Phlebia, Grandinia, Odontia, Kneiffia)andAuricularini (Craterellus, must be mentioned. Jacques Boidin has added valuable charac- Thelephora, Stereum, Hymenochaete, Auricularia, Corticium, ters for taxonomy through his studies of culture characteris- Cyphella). His classification also gives a glimpse of what genera tics, mating systems, and nuclear behaviour. Kurt Hjortstam were most widely used during the 19th century. In mycology has followed Donk and Eriksson, and contributed numerous the entrance of a new century was marked by the extraordinary new genera. Boidin and Hjortstam have also pioneered the con- publication Essai taxonomique des Hyme´nomyce`tes (Patouillard temporary exploration of tropical corticioid diversity by col- 1900). This book presented a new classification that broke with lecting and describing new species and by reviving many old the Friesian tradition and introduced many of the concepts still and ignored names introduced by 19th century mycologists. widely used. For example, Patouillard divided the Hymenomy- A new classification for the fungi down to order is now cetes into Hetero-andHomobasidiomycetes and divided the latter available as the result of an international cooperation, and into ‘Agaricace´s’ and ‘Aphyllophorace´s’. Patouillard’s classifica- that unified classification is fully adopted here (Hibbett et al. tion became the foundation for taxonomic mycology for almost 2007). The object of the present paper is to elaborate on a clas- 100 y. When Donk published his conspectus of the families of sification for corticioid fungi at family level, drawing on recent Aphyllophorales (Donk 1964)hequotedPatouillardastheprime achievements through molecular phylogenetic analyses and inspiration. Donk (1964) tried to carve out ‘natural groups’ using taking into account only monophyletic groups. It is my hope all the information on morphology and cytology available at that that the hypotheses put forward here, subjective as they time. He preferred evolution rather than revolution and may be, will stimulate further investigations and encourage accepted 21