Systematics of Lactarius in the Rocky Mountain alpine zone
Barge, Edward Gilman.
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Lactarius is an important component of the ectomycorrhizal community in cold-dominated arctic and disjunct alpine habitats where it associates primarily with the woody shrubs Betula, Dryas, and Salix. Little is known of the alpine fungi in the central and southern (Montana, Wyoming, Colorado) Rocky Mountain alpine zone (elevation 3,000-3,900 m) of North America. The goal of this study was to examine the genus Lactarius and here at least six species from subgenera Russlularia and Piperites are confirmed above treeline through molecular phylogenetic analyses of ITS and rpb2 DNA in conjunction with detailed morphological examination. All (except two putative new species) appear to have broad intercontinental distributions in North America and Eurasia according to molecular comparison with type material, and collections from Europe, Greenland, Scandinavia, Svalbard, and Alaska. Rocky Mountain alpine collections of L. lanceolatus and the type from Alaska form a well-supported clade paraphyletic with respect to well-supported clades consisting of L. aurantiacus and several North American subalpine taxa. Rocky Mountain alpine collections of L. nanus, L. glyciosmus, L. repraesentaneus, and L. salicis-reticulatae all form well-supported clades with material from European type localities and other arctic-alpine material; although some clades contain nested (L. hysginoides within L. nanus) and possibly cryptic species (L. aff. salicis-reticulatae from Colorado). The well-known arctic-alpine L. pseudouvidus/L. brunneoviolaceus group of violet-staining species appears to be a complex possibly containing additional species. North American material originally described as part of this group, is well-separated phylogenetically and represents a putative new species (L. pallidomarginatus Barge & C.L. Cripps ad int.) so far confined to the Southern Rockies with shrub Salix. The monophyly of the violet-staining section Uvidi is supported. Lactarius lanceolatus, L. nanus, and L. salicis-reticulatae appear largely restricted to arctic-alpine habitats across their broad range, where they associate with dwarf and shrub Salix. Lactarius glyciosmus and L. repraesentaneus are not restricted to arctic-alpine areas and occur with Betula and krummholz Picea (possibly also Salix), respectively in the Rocky Mountains; the latter is also known with Betula in broader parts of its range. Species distributions are hypothesized to be tied to host ranges, glaciation, and long distance dispersal.