MYCOLEGIUM: Making Sense New Mushroom Genera: of a Ll T He Ne W Horn of Plenty Or Deluge? Mushroom Names Else C
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Courtesy M. G. Wood. MYCOLEGIUM: Making Sense New mushroom genera: of a ll t he Ne w horn of plenty or deluge? Mushroom Names Else C. Vellinga and Thomas W. Kuyper [email protected] n 2014 and the first Text box #1 – Some definitions six months of 2015 clade – a monophyletic group consisting of a common ancestor and all its descendants. alone, more than 20 genus (plural: genera) – a monophyletic group of species that have (preferably) new bolete genera were morphological characters in common. I monophyletic – a genus is called monophyletic when all its members share a proposed. Contrary to what most recent common ancestor that is not shared by species outside that many people would expect, these genera genus (the red and blue blocks in Fig. 1 represent monophyletic groups). are not restricted to some faraway exotic A single species is monophyletic by definition. locale where the boletes have novel paraphyletic – a genus is called paraphyletic, when only by including members character combinations, no, these new of another genus or other genera, all its members share a common ancestor genus names are for familiar species that (the green block in Fig. 1 represents a paraphyletic genus). occur in North America and Europe and polyphyletic – a genus is called polyphyletic as a more advanced case of that we have been calling by the name paraphyly and the members of the genus are scattered over widely different “Boletus” for a long time. clades (example: Marasmius with M. androsaceus falling inside Gymnopus, This creation of new genera is not and M. minutus outside the family Marasmiaceae). restricted to the boletes. The numbers sister group – the closest relative of a clade or species in a phylogenetic tree for the gilled mushroom species are (the red block in Fig. 1 is a sister group to the blue-green clade). comparable: we counted around 24 new genera published in that same time taxon (plural: taxa) – any taxonomic unit from forma to phylum. period, most of them white-spored, type species of a genus – the species that is the name-bearing type of a genus with six new genera for species we used (example: Coprinus comatus is the type species of the genus Coprinus; when to call Clitocybe, five new genera in the Coprinus was split up, the name Coprinus stayed with C. comatus, and the Lyophyllaceae, and three new ones in the other parts of the genus, got new names). The type species is not Psathyrella family. However, there were necessarily the most typical for the genus. only two new brown-spored genera. And the largest genus by far, Cortinarius, was not affected. Most of these genera are for existing species, only a few, such as Cercopemyces crocodilinus from the Rocky Mountains (Baroni et al., 2014; and see the spring 2015 issue of FUNGI), are for newly discovered species. Here we will try to explain what triggered this flood of new genera. We’ll also have a critical look at what is necessary to make good, solid, acceptable genera. On that basis we can also look Figure 1. An example of a phylogenetic tree with the terminal branches each critically whether these new genera are, representing an individual species. The blue and the red parts of the tree at least for the time being, warranted. represent monophyletic groups. The green part is not monophyletic, but We give references to the original paraphyletic, as the green and the blue together are monophyletic. The red articles in which the research we cover clade is sister to the green/blue clade. (from Wikimedia) here is described; many of those are freely accessible, so you can see for Some historical background with the underlying principle that what yourself how this type of science is done. Up to the mid 1990s mushroom we recognized represented a natural Definitions of some of the terms we use genera were recognized and described system and that system was the result throughout this article are in Text box #1. based on morphological characters, of evolution. These classifications were FUNGI Volume 8:4 Winter 2015 35 of course subjective and prone to a lot characters that could be used to gauge your family tree one could conclude of debate. Different traditions reigned the value of certain characters for that your cousin is your closest on the different continents: Entoloma in genus definitions. What to do with relative, though in reality it is your Europe included Nolanea and Leptonia, those characters that were incongruent brother. So trees that are based whereas in the USA these were three was a big problem. Was it more exclusively on taxa of a certain area different genera, and Hygrophorus in important that all species in a genus had (e.g., the northern hemisphere), North America included the colorful amyloid spores than that they all were while the group itself has a much Hygrocybe species that were in their own ectomycorrhizal or had an annulus? broader geographical distribution, genus in Europe. Those were unanswerable questions, as in the case of some bolete trees, Name changes happened, also in the though, of course; taxonomists would are suspect. past. An example is the turkey tail, now argue about these issues, but nobody 2. Is your tree a gene tree, based on known as Trametes versicolor, which has could claim victory. one piece of DNA only, or is it resided in 12 different genera since its Molecular phylogenetics changes based on a critical examination of a initial naming in 1753 (Linnaeus, 1753). fungal systematics number of different genes? And if it Alexander Smith was upset by the is based on one piece of DNA only, With the advance of molecular flood of new genera created by Singer is that a piece that is known to be methods to make many copies of pieces who worked in the neotropics where the very variable and very helpful at the of DNA that could then be analyzed mushrooms did not fit the descriptions species level but not so much for and sequenced, and the development of of the temperate genera. Smith (1968) genus recognition? The nrITS region larger and faster computers that could thought that “When we have made a (a spacer region that sits in between deal with larger and more complicated critical study from an adequate sample genes that do not show much data sets, mushroom systematics of a population, such as that of North variation among species) is very changed dramatically. America for the gill fungi, I believe that good at discriminating mushroom These methods made it possible to the generic concepts will be found to be species (not all, but many; it is compare genetic markers (for instance rather self-evident.” therefore used as the so-called bar pieces of spacer regions in between Mushroom fruitbodies do not have code region. But while it is very genes, and genes that code for the a wealth of morphological characters, good at species, that means there is household chores in the cells, but not so they did not lend themselves very a lot of variation among species, and those that make the pigments) and we well to phylogenetic studies based on it is much harder to use for species could formulate hypotheses for the morphology as developed by Hennig groups that are not so closely evolution of these pieces of DNA. These (1950; 1965). There were simply no related. The nrITS region is not hypotheses are in general presented recommended as the sole marker as a phylogenetic tree, in which each for genus recognition. Unfortunately terminal branch is a sample or a (or should we say of course) some collection. The more different pieces of mycologists still do base genera on DNA that are used to make these trees, trees derived from ITS data alone. the more species and specimens are A further advantage of making trees included, and the higher the statistical based on a number of (say 5–8) support for the branches on the tree is, genes, is that it allows evaluation of the better this hypothesis will represent alternative classifications in case the the true path of evolution. The tree various genes provide contradictory might become a species tree instead of information. If statistical support for a gene tree. These trees are similar to the final tree is low, an attempt can the family trees one can build for their be made to analyze the causes for ancestors, though here the terminal that lack of congruence. branches represent an individual person. These phylogenetic trees are used to The first revolutionary results determine what good species are, and Coprinus, the inky cap genus, was one also for the circumscription of genera. of the first genera to be analyzed with Figure 2. A phylogenetic tree with 5 As indicated above, one needs to look these new methods, and to everybody’s terminal monophyletic taxa. This tree carefully at the tree, and be aware of a surprise this genus turned out to be represents many different monophyletic few things: polyphyletic, with Coprinus comatus genera: a; a and b together; a, b and c 1. Which taxa are included in the tree? and its close allies closely related to together; a, b, c, and d together, and all One can only draw conclusions Lepiota, and the rest of the genus not five together. A paraphyletic genus is about the taxa that are included in monophyletic, but clearly separating formed by the d-e combination, or by the study, not about those that are into three groups (Hopple and Vilgalys, c, d and e; the combination of a and e not there – it is like making a family 1999).