Improved resolution of major clades within Tuber and taxonomy of species within the Tuber gibbosum complex

Abstract

Tuber gibbosum Harkn., described from northern California, originally was thought to be a single, variable species that fruited from autumn through winter to spring. It has become popular as a culinary truffle in northwestern USA, where it is commercially harvested. Morphological studies suggested it might be a complex that includes at least two species. We conducted morphological and phylogenetic studies of the complex to determine how many species it might contain and how they differed morphologically, geographically and seasonally. We also provide the first LSU phylogeny for the genus Tuber. Phylogenetic analyses resolve nine major clades in the genus with high bootstrap support and distinguish the Gibbosum clade from the Aestivum, Excavatum, Macrosporum, Magnatum, Melanosporum, Puberulum, Rufum and Spinoreticulatum clades. Further analyses of ITS and LSU regions revealed four distinct species in the Gibbosum complex. Although morphologically similar the four species differ in spore size and shape and in peridial anatomy. These species share the synapomorphy of having suprapellis hyphae with distinctive, irregular wall swellings at maturity; we have not seen this hyphal type in any other Tuber spp. worldwide. The three new species are named and described as T. bellisporum Bonito & Trappe, T. castellanoi Bonito & Trappe and T. oregonense Trappe, Bonito & Rawlinson.

• Ascomycota
• hypogeous fungi
• ITS
• LSU
• mycorrhizae
• Oregon white truffle
• Pezizales
• phylogeny
• Tuberaceae

We thank the North American Truffling Society and other collectors who provided the material used in this research, Matt Trappe for providing valuable field support, A. Montecchi for donating a specimen of his interesting and apparently undescribed Tuber species, Rosanne Healy for guidance on electron microscopy and collection loans, Michael Castellano for discussions helpful to this paper, Conrad Schoch, Kentaro Hosaka and Doni McKay for lab assistance, and Joey Spatafora and Richard Halse of the Oregon State University Department of Botany Herbarium for extensive herbarium services, including accession of the collections cited here plus many addition collections. Welles Bushnell, Adrian Beyerle and Sylvia Donovan contributed immensely to organizing and preparing the collections for herbarium accession. The National Fungus Collections and Herbarium of the Università di Bologna generously lent additional collections for study. This research was supported through NSF award number 0641297, REVSYS: Phylogenetic and Revisionary Systematics of North American Truffles (Tuber).