Biology of the ectomycorrhizal genus Rhizopogon. V. Phylogenetic relationships in the Boletales inferred from LSU rDNA sequences

The phylogenetic relationship between Alpova, Chroogomphus, Gomphidius, Rhi zopogon, Suillus, and Truncocolumella and their placement in the Boletales was tested through maximum parsimony analyses of large subunit nuclear ribo somal DNA sequences. Taxon sampling included representatives of the genera Alpova, Boletellus, Boletus, Chroogomphus, Gomphidius, Melanogaster, Paragy rodon, Phylloporus, Rhizopogon, Suillus, Truncocolumella, Tylopilus, and Xe rocomus, as well as species from the Agaricales, Russulales, and Polyporale s. The order Boletales was strongly supported as monophyletic. Furthermore, within this order, two major groups emerged: the boletoid radiation and a Melanogastraceae/Paragyrodon sphaerosporus paraphyletic assemblage, and the suilloid radiation. The boletoid radiation and a Melanogastraceae/Paragyro don sphaerosporus assemblage was strongly supported. Although the boletoid radiation was not strongly supported by bootstrap analysis, the clade did n ot collapse in the strict consensus topology. This clade comprised species from the genera Boletellus, Boletus, Phylloporus, Tylopilus, and Xerocomus. The Boletaceae sensu Singer was not monophyletic. Although species relatio nships within the boletoid radiation were not well resolved, the genus Bole tus did not appear to be monophyletic. Alpova diplophloeus, A. trappei, Mel anogaster tuberiformis, and Paragyrodon sphaerosporus formed a paraphyletic assemblage basal to the boletoid radiation clade. The suilloid clade was s trongly supported and included Alpova olivaceotinctus, Chroogomphus, Gomphi dius, Rhizopogon, Suillus and Truncocolumella citrina. Species in the genus Alpova therefore were grouped both within and outside the suilloid radiati on. Within the suilloid radiation, Suillus was inferred to be more closely related to Truncocolumella citrina and the Gomphidiaceae than to Rhizopogon , suggesting a more distant relationship between Suillus and Rhizopogon tha n previously hypothesized. Rhizopogon was not supported as monophyletic, al though its monophyly could not be rejected by the data. Alpova olivaceotinc tus grouped within the genus Rhizopogon, consistent with previous classific ations, and is returned to that genus.