In Colombia the Eurasian fungus <i>Amanita muscaria</i> is expanding its range into native, tropical <i>Quercus humboldtii</i> forests VargasNatalia GonçalvesSusana C. Franco-MolanoAna Esperanza RestrepoSilvia PringleAnne 2019 <p>To meet a global demand for timber, tree plantations were established in South America during the first half of the 20th century. Extensive plantings of non-native species now are found in Brazil, Chile, Argentina, and Uruguay. In Colombia, miscellaneous plantations were established in the 1950s, during a period of intensive local logging, when policies to limit deforestation in native <i>Quercus humboldtii</i> forests were established. One unforeseen consequence of planting non-native trees was the simultaneous introduction and subsequent persistence of ectomycorrhizal fungi. We sought to document the origins and spread of the introduced <i>Amanita muscaria</i> found in Colombian plantations of the Mexican species <i>Pinus patula</i>, North American species <i>P. taeda</i>, and Australian species <i>Acacia melanoxylon</i> and <i>Eucalyptus globulus</i>. In Colombia, <i>Amanita muscaria</i> is establishing a novel association with native <i>Q. humboldtii</i> and has spread to local <i>Q. humboldtii</i> forests. According to a Bayesian phylogeny and haplotype analysis based on the nuclear rDNA internal transcribed spacer region ITS1-5.8-ITS2 (ITS barcode), <i>A. muscaria</i> individuals found in four exotic plant species, and those colonizing <i>Q. humboldtii</i> roots, have a Eurasian origin and belong to two Eurasian haplotypes. This is the first time the spread of an introduced mutualist fungus into native Colombian <i>Q. humboldtii</i> forests is reported. To arrest its spread, we suggest the use of local inocula made up of native fungi, instead of inocula of introduced fungi.</p>