Book Review

A Preliminary Monograph of Lentinellus (Russulales)

By Ronald H. Petersen and Karen W. Hughes
Bibliotheca Mycologica Band 198, 2004
ISBN 3-443-59100-0
80 euros (softcover, 268 pages, plus index and 13 color plates)

The Xerula/Oudemansiella Complex (Agaricales)

By Ronald H. Petersen and Karen W. Hughes
Nova Hedwigia Beiheft 137, 2010
ISBN 978-3-443-51059-6
179 euros (hardcover, 625 pages, including 31 color plates)

Over the past 2 years, I have made several collecting trips to Great Smoky Mountains National Park, working on a project led by Dr. Brandon Matheny of the University of Tennessee and Inocybe fame. To get to Brandon’s lab, one has to pass the office of Ron Petersen and, nearly every time I have walked by, Ron has been hunkered over his microscope hard at work - you would never guess that this Professor Emeritus is retired. Across the hall, Karen Hughes usually is busy in her office deciphering DNA sequences. Together, this pair has accomplished a tremendous amount of work, trying to unravel the evolution and relationships of the mushroom-fungi through melding of traditional morphological taxonomy, mating studies, (both Ron’s bailiwick) and the more recently developed molecular methods (Karen’s). These two substantial monographs provide evidence of two of their recent projects.

Although structured a bit differently from each other, both volumes include the same three major parts - monographic descriptions of taxa and keys to them, description and assessment of type collections, and results of molecular phylogenetic analyses.

The descriptions in the monographic sections typically include the name, with complete authority, references to illustrations in the volume, lengthy list of synonyms, references to illustrations in other works, comprehensive recitation of macroscopic and microscopic features, habitat summary, extensive valuable commentary, and list of collections studied. In Lentinellus, the descriptions also include extensive information about culture characteristics and mating experiment results. Descriptions are mostly 3 to 6 pages long, but many exceed that. I am perhaps most impressed by the lists of collections. Ignoring the logistics challenge of obtaining them, the large number, combined with the lengthy detail in the observations, explains why Ron spends so much time hunched over his scope!

The information presented in the type studies sections is generally similar, although arranged in simpler fashion. The original source and herbarium location of the collection are given, followed by macroscopic and microscopic observations of the material, and commentary. Regardless of how one views the authors’ taxonomic decisions, the wealth of descriptive and interpretive information contained in the monograph and type studies sections of these two books represents a long-term resource of great value and Ron and Karen are to be commended for compiling it.

The keys in both volumes are dichotomous and rely heavily on microscopic features. In Lentinellus, the leads typically involve single features, which I dislike, as there are times when that feature is unclear in the material one is working with. However, in my initial trials, the keys worked well. The leads in Xerula mostly involve multiple features and seem workable, although I didn’t have an opportunity to try them as I live in a Xerula/Oudemansiella-free part of the country.

As for the illustrations ... just let me say these aren’t books you are likely to display on your coffee table. Field mycology is very time-consuming and when collecting is good, there is no way anyone has the time to find material, do good field photography, and make detailed observations and descriptive notes, while hoping to also find time for eating and sleeping. Thus, like most books produced by professional mycologists, the color photos are mostly sterile line-up shots (31 in Lentinellus, 45, plus five reproductions of historic illustrations, in Xerula) that, although generally serviceable, are not real eye-grabbers. Lentinellus also has a handful of black and white photos, as well as numerous well rendered drawings of spores, cystidia, basidia, and hyphae that accompany the descriptions. Xerula has similarly excellent microfeature drawings, and many of them are accompanied by effective line-drawings of whole fruitbodies. A rather annoying feature of Lentinellus is the placement of the legends for the color plates—although the plates themselves appear at the very end of the book (following page 270), the legends are on page 179 (at the end of the monograph section).

In Lentinellus, the authors accepted 24 species, at least 12 of which occur in North America—L. castoreus, cochleatus, cystidiosus, flabelliformis, micheneri, montanus, occidentalis, semivestitus, subargillaceus, subaustralis, ursinus, and vulpinus. The basis for recognition of the different species varies from one to another, sometimes emphasizing morphology, sometimes mating experiment results, and, at other times, the molecular phylogenetic data. The authors do a good job of explaining why they made the decisions they did, allowing the reader to decide for him/herself whether or not to agree. Certainly the lengthy descriptive information in the volume will provide a good basis upon which to base such decisions. In listing illustrations of the species, the authors chose not to include many that appear in popular books, on the basis that the identifications could not be verified. While understandable, I would have preferred them to provide assessments of those illustrations—what species (singular or plural) do they think is/are represented? I have always maintained that if it cannot be determined from a good-quality documentary photograph which of two species is portrayed, then the photo could be used to represent either of them equally well. Nonetheless, this argues for more mushroom-photographers adopting the practice of making voucher collections to support their photos. This also would have the benefit of making many very attractive photos available for technical works.

In Xerula, the authors accepted 69 named species (four of them newly described) plus two un-named species and a number of forms. These are distributed among 8 genera, 4 of them newly described, and only two—Oudemansiella and Xerula—likely to be familiar to most non-specialists. The new genera are Hymenopellis, Paraxerula, Ponticulomyces, and Protoxerula. The previously coined genus names Dactylosporina and Mucidula also were resurrected. For those of us in North America, though, things aren’t as bad as they might appear, for the 10 named and one un-named species that occur here are in only four of the genera—Hymenopellis (H. furfuracea, incognita, limonispora, megalospora, rubrobrunnescens, rugosoceps, sinapicolor, and “species 1”), Oudemansiella (O. canarii), Paraxerula (P. americana, known from the Rocky Mountains as X. longipes), and Xerula (X. hispida, which occurs in Mexico and points south). Other than the last two, all are eastern species.

Most of the analyses suggested to the authors that species distinctions were fairly clear. However, the same could not be said of their attempts to sort them into genera—in particular, the phylogenetic trees were problematic when viewed in conjunction with the morphologic data (mating studies were not an issue here). Nowadays it is likely that most workers would have followed the phylogenetic analyses faithfully, and applied names only to monophyletic groups. Here this was not done (in particular, Hymenopellis was adopted for a paraphyletic group of species) and for reasons that seem sound to me, although others certainly will disagree. Nonetheless, I don’t like the decision to create several new genera and make a large number of new combinations when there are unresolved questions about the correspondence between the different types of data. Better to go slowly with the name changes until it is likely that they will be lasting, not transient, ones.

If it isn’t already clear, these books are not for the casual mushroom-hunter—they are for the professionals and those amateurs with a serious interest in the taxonomy of these groups. Those folks will find them very useful. Eventually, though, their influence will be felt in the amateur community as field guides and popular websites incorporate their findings. However, as is too often the case with technical publications, the high prices will undoubtedly limit sales and greatly lengthen the time it takes for the information to make it into the mushroom mainstream.

— Review by Steve Trudell, Seattle, WA
— Originally published in Fungi