Impacts of New Knowledge on Mushroom Phylogeny

Recent advances in classification of fungi, an outcome of a national research program on the Tree of Life and related projects, are changing our view of how different mushroom forms are related and how these changes affect scientific names.

The Fungal Tree of Life

The Fungal Tree of Life project was designed to develop a comprehensive phylogenetic tree for fungi, using molecular and structural characters. A phylogenetic tree reveals relationships among species just as a genealogical tree reveals the relationships between members of our family and connections to other people’s families. A phylogenetic tree has predictive value, helping to explain changes among species in their form, internal structure and ecological relationships just as a genealogical tree explains facial and other physical similarities as well as our susceptibility to some ailments. The goal of the Tree of Life projects is to provide a classification that reflects the actual relationships among species.

Nineteenth Century Classifications:  Simple But Unnatural

AscusMushrooms are produced by two great groups (phyla) of fungi, the Ascomycota or sac fungi and the Basidiomycota or club fungi. The names for these groups refer to the mushroom structures that produce their sexual spores. We will focus here on the club fungi, specifically the gilled (agarics), nongilled (boletes, polypores, coral fungi, teeth fungi, and chanterelles) and the gasteroid (puffballs, earthstars, bird’s nest fungi, stinkhorns and false truffles) mushrooms. They were classified in the 19th century in three large groups (orders or class): the Aphyllophorales for nongilled mushrooms, the Agaricales for gilled mushrooms and the Gasteromycetes for gasteroid forms, whose fruiting bodies remained closed until maturity.  This was a convenient classification system for mushrooms because it required only the external form of the mushroom to classify them, but it also disguised who is related to whom.Basidium

EarthstarTeeth FungusAgaric

The Fungal Tree of Life project has upended the earlier classification with mushrooms now spread across 14 orders and with many different mushroom forms in each order.  Below is a current phylogenetic tree of the Agaricomycotina as of 2012, which includes the familiar mushroom-forming Basidiomycetes.

Major Clades
             

New Classifications:  Confusing But Necessary

Naturally, this has an impact on the scientific names of mushrooms. A good example is the inky caps. Formerly all inky caps were classified in a single genus Coprinus, which was distinguished by its black spores and self-digesting gills that produce the “ink”. Coprinus was placed in the family Coprinaceae with some other black-spored mushrooms, such as Psathyrella, which lacks the inky gills. Coprinus
The Fungal Tree of Life studies revealed that Coprinus was actually four groups (genera) of mushrooms that had independently developed the ability to form inky caps. Three were related to each other and to Psathyrella, but the fourth was related to the button mushroom Agaricus, including the type of Coprinus, i.e., the species to which the genus name is attached. Coprinus was then transferred to the family Agaricaceae. Thus, we ended up with the family Coprinaceae without Coprinus and a new family name was chosen Psathyrellaceae for the remaining three groups of inky caps, each with a new genus name, and Psathyrella as the type of the new family.

Agaricus PlacyomycesCoprinellus MicaceusPsathyrella Candolleana

These name changes are disconcerting for the scientist and non-scientist alike but they lead to greater stability in names in the long run and a better understanding of the organisms.

Supported by the National Science Foundation Assembling the Fungal Tree of Life awards DEB-0228671 and DEB-0732550 to D.J. McLaughlin.  Drawings by Debra Greenblatt.