Ganoderma is a large, diverse and globally-distributed genus in the Basidiomycota that includes species causing a white rot form of wood decay on a variety of tree species. For the past century, many studies of Ganoderma in North America and other regions of the world have used the name G. lucidum sensu lato for any laccate (shiny or varnished) Ganoderma species growing on hardwood trees or substrates. Molecular studies have established that G. lucidum sensu stricto (Curtis) Karst is native to Europe and some parts of China. To determine the species of the laccate Ganoderma that are present in the United States, we studied over 500 collections from recently collected samples and herbarium specimens from hardwoods, conifers, and monocots. A multilocus phylogeny using ITS, tef1α, rpb1 and rpb2 revealed three well-supported clades, similar to previously reported findings. From the U.S. collections, thirteen taxa representing twelve species were identified, including: G. curtisii, G. lucidum sensu stricto, G. martinicense, G. oregonense, G. polychromum, G. ravenelii, G. sessile, G. tsugae, G. tuberculosum, G. cf. weberianum, G. zonatum, and Tomophagus colossus (syn. G. colossus). The species G. meredithiae is synonymized with G. curtisii, and considered a physiological variant that specializes in decay of pines. The designation G. curtisii f.sp. meredithiae forma specialis nov. is proposed. Species such as G. curtisii and G. sessile, once considered as G. lucidum sensu lato, were found to be divergent from one another, and highly divergent from G. lucidum sensu stricto. Morphological characteristics such as context tissue color and features (e.g. melanoid bands), basidiospore shape and size, geographic location, and host preference were found to aid in species identification. Surprisingly, G. lucidum sensu stricto was found in the U.S., but only in geographically restricted areas of northern Utah and California. These collections appear to have resulted from the introduction of this species into the United States possibly from mushroom growers producing G. lucidum outdoors. Overall, this study clarifies the chaotic taxonomy of the laccate Ganoderma in the United States, and will help to remove ambiguities from future studies focusing on the North American species of laccate Ganoderma.
Bibliographical noteFunding Information:
This project was funded in part by the F. A. Bartlett Tree Experts Company and a research grant from the International Society of Arboriculture-Florida Chapter and was also supported in part by the USDA National Institute of Food and Agriculture, Hatch project 0022081. Matthew E. Smith’s involvement in this project was made possible by the support of the Institute of Food and Agriculture Sciences at the University of Florida and by a grant from the National Institute of Food and Agriculture, USDA, under the grant #FLAPLP-005289. Finally, the herbarium studies were made possible by the Clark T. Rogerson research award from the Mycological Society of America. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. The first author Andrew Loyd is employed by the F.A. Bartlett Tree Experts Company. F.A. Bartlett Tree Experts Company provided support in the form of salary for author AL, but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific role of this author is articulated in the ‘author contributions’ section. We are extremely grateful to Ryan Gates, Neil Dollinger, Jason Conheeney, Eric Otto and all of the many citizen scientists who submitted collection material for study as well as Drs. Guido Schnabel, Julia Kerrigan, Monica Elliott, and James Jacobs for Ganoderma cultures and collections. We are also grateful to the mycological herbaria at the University of Florida (FLAS) and North Carolina State University (NCSCLG) for allowing us to study their collections. We would also like to thank Cassondra Newman, Eric Linder, Sam Redford, Connor Lund, Camille Schlegel and Liam Genter for assistance in DNA extractions and sequencing. Also, we are grateful for two sequences from Bob Johnson and Dave Rizzo from UC Davis.