A multi-gene phylogeny of <i> Lactifluus</i> (<i>Basidiomycota</i>, <i>Russulales</i>) translated into a new infrageneric classification of the genus

Infrageneric relations of the genetically diverse milkcap genus <i>Lactifluus</i> (<i>Russulales</i>, <i>Basidiomycota</i>) are poorly known. Currently used classification systems still largely reflect the traditional, mainly morphological, characters used for infrageneric delimitations of milkcaps. Increased sampling, combined with small-scale molecular studies, show that this genus is underexplored and in need of revision. For this study, we assembled an extensive dataset of the genus <i>Lactifluus</i>, comprising 80 % of all known species and 30 % of the type collections. To unravel the infrageneric relationships within this genus, we combined a multi-gene molecular phylogeny, based on nuclear ITS, LSU, <i>RPB2</i> and <i>RPB1</i>, with a morphological study, focussing on five important characteristics (fruit body type, presence of a secondary velum, colour reaction of the latex/context, pileipellis type and presence of true cystidia). <i>Lactifluus</i> comprises four supported subgenera, each containing several supported clades. With extensive sampling, ten new clades and at least 17 new species were discovered, which highlight the high diversity in this genus. The traditional infrageneric classification is only partly maintained and nomenclatural changes are proposed. Our morphological study shows that the five featured characteristics are important at different evolutionary levels, but further characteristics need to be studied to find morphological support for each clade. This study paves the way for a more detailed investigation of biogeographical history and character evolution within <i>Lactifluus</i>.