Assessing biogeographic relationships between North American and Chinese macrofungi

Aim: A close biogeographic relationship between the macrofungi of eastern North America and eastern Asia has been documented based on comparisons of species lists. In addition to having a similar species composition, the two regions are reported to share a number of species with putative disjunct distributions. This close biogeographic relationship, however, has rarely been tested within a phylogenetic context. In this paper we examine relationships within three genera, Armillaria, Xerula and Suillus (Fungi, Basidiomycetes, Agaricales) chosen as exemplars of different ecological guilds occupied by macrofungi (plant pathogens, saprobes, mutualists). Location: Fieldwork for this project centered in eastern North America, Central America, China and Australasia. Material from additional localities were obtained from cooperating herbaria and additional sequences were downloaded from GenBank. Methods: ITS sequence data were used to construct phylogenies for each genus. Results: Only one of four tested putative disjunct species, Xerula hispida Halling and Mueller, was supported. Material referable to X. furfuracea (Peck) Redhead, Ginns and Shoemaker from China and North America do not form a monophyletic group. Disjunct populations of Suillus spraguei (Berkeley & Curtis) Kuntze were shown to be paraphyletic. The morphological similarity of the Chinese material to the North American material is likely due to morphological stasis. Finally, morphologically identical material referable to Suillus americanus (Peck) Snell in Slipp and Snell from eastern North America and S. sibiricus (Singer) Singer from China, along with the morphologically similar western North American S. sibiricus, probably represent a single circumboreal taxon. Main conclusions: The resulting data, while not refuting the hypothesis that there exists a relatively close biogeographic relationship for macrofungi between eastern North America and eastern Asia, suggest that the relationship may not be as close as indicated by morphological data. These results are similar to emerging data from analyses of flowering plants displaying putative eastern North American/eastern Asian disjunct distribution patterns.