Unearthing two new ectomycorrhizal Pezizales truffle species from Nothofagaceae forests in southern South America

Truffles are enclosed, hypogeous fruiting bodies that have evolved hundreds of times across different fungal groups. Truffles are particularly diverse within Pezizales, a large and diverse order of Ascomycota where truffle forms have evolved multiple times. The majority of truffle species are ectomycorrhizal symbionts of trees and rely on animals for dispersal. Because of their hypogeous nature, truffles remain understudied and many new taxa remain to be discovered. Due to their obligate symbiosis with host plants and their dependence on animal dispersal, ectomycorrhizal truffle species often show distinct host associations, are restricted to certain forest types, and have notable biogeographic distribution patterns. Here, we present morphological and phylogenetic evidence in support of two new truffle species associated with Nothofagaceae trees in southern South America, <i>Geomorium nahuelbutense</i> (Geomoriaceae) and <i>Paragalactinia nothofagacearum</i> (Pezizaceae). The closest described relatives of these species form aboveground, apothecial ascomata, suggesting that these taxa are derived from independent evolutionary events leading to the truffle morphology. <i>Paragalactinia nothofagacearum</i> is widespread in northern Patagonia and has been documented as an ectomycorrhizal associate of <i>Lophozonia alpina</i> (= <i>Nothofagus nervosa</i>) seedlings. In contrast, <i>Geomorium nahuelbutense</i> has only been found in a well-preserved coastal forest in Chile toward the northern extent of the range of Nothofagaceae in South America. This is a conservation priority area that has been heavily impacted by fires, deforestation, and other human activities. This species is known only from two modern collections from Parque Nacional Nahuelbuta and one preserved specimen collected by Roland Thaxter near Concepción, Chile, in 1906.