Recent taxonomic discoveries suggest a host-symbiont co-migration of Russula subsect.Castanopsidum with Fagaceae in the Americas: alignments and tree files

Three members of ectomycorrhizal fungi belonging to <i>Russula</i> subsection <i>Castanopsidum</i> are described from neotropical montane forests dominated by species of <i>Fagaceae</i> in Panama and Colombia. <i>Russula esperanzae</i> sp. nov. from Colombia differs in the field from other members of the subsection by slender longitudinally striated red stipes as well as characteristics of spores and basidia. <i>Russula atroamethystina </i>subsp. <i>atroamethystina,</i> originally described from Costa Rica, is reported for the first time from Panama. Closely related and morphologically similar Colombian collections are described as <i>R. atroamethystina </i>subsp. <i>guacahayoensis</i> subsp. nov. and differ from the typical subspecies by longer hymenial cystidia as well as molecular sequence data. The distribution of this newly described subspecies is restricted to <i>Fagaceae</i> forests east of the Isthmus of Panama. This suggests an allopatric diversification, likely driven by the absence of <i>Fagaceae</i> in the tropical lowland forest of the Darién Gap. <i>Russula esperanzae</i> is exclusively associated with <i>Trigonobalanus excelsa</i>, a tree species of <i>Fagaceae </i>endemic to Colombia. The role of its association with this tree in the evolutionary history of the species is discussed. Based on molecular timing, species of the subsection <i>Castanopsidum</i> started to evolve approximately 15.1 million years ago (mya) and display an amphi-pacific disjunct distribution with an Asian clade that split from the American clade around 11 mya.