New insights in Russula subsect. Rubrinae: phylogeny and the quest for synapomorphic characters

Abstract

Russula is one of the most speciose genera of mushroom-forming fungi, but phylogenetic relationships among species and subgeneric groupings are poorly understood. Our multi-locus phylogenetic reconstruction places R. firmula, R. rubra, R. rutila and R. veternosa in a well-supported Rubrinae clade, belonging to the Integrae clade of the Crown clade of the genus Russula. Traditional morphology-based classifications placed these four species in two different subsections based on the presence or absence of incrustations on pileocystidia. The Integrae clade also contains R. integra and related species that are traditionally placed in other groups based on their mild taste. Ancestral state reconstruction suggests that the common ancestor of the Crown clade and the Integrae clade probably did not have any incrustations in the pileipellis, had a mild taste, yellow spore print and were associated with angiosperms. All four species of the Rubrinae clade are defined by a darker yellow or ochre spore print, acrid taste and incrustations on pileocystidia. This last character contradicts the former splitting of the group because incrustations were apparently overlooked in R. firmula and R. veternosa. Incrustation type is now highlighted as being important for the delimitation of species and groups within the Crown clade. Pink or red staining of the incrustations in sulphovanillin is present in all species of the Rubrinae clade and a majority of the analysed species of the Integrae clade. The delimitation of the Rubrinae clade and its species circumscriptions are summarised here in a new diagnostic key.