From White to Black, from Darkness to Light: Species Delimitation and UNITE Species Hypothesis Testing in the Russula Albonigra Species Complex.

Abstract

Russula albonigra is considered a well-known species, morphologically delimited by the context of the basidiomata that is blackening without intermediate reddening, and the menthol-cooling taste of the lamellae. It is supposed to have a broad ecological amplitude and a large distribution area. A thorough molecular analysis based on four nuclear markers (ITS, LSU, RPB2 and TEF1-α) shows this traditional concept of R. albonigra s.l. represents a species complex consisting of at least five European, three North-American and one Chinese species. Morphological study shows traditional characters used to delimit R. albonigra are not always reliable. Therefore, a new delimitation of the R. albonigra lineage is proposed and a key to the described European species of R. subg. Compactae is presented. A lectotype and an epitype are designated for R. albonigra and three new European species are described: R. ambusta, R. nigrifacta and R. ustulata. UNITE species hypotheses at different thresholds were tested against the taxonomic data. The species hypotheses at the similarity threshold 0.5% give a perfect match to the phylogenetically defined species within the R. albonigra lineage. Publicly available sequence data can contribute to species delimitation and expand knowledge on ecology and distribution, but the pitfalls are short and low quality sequences. The importance of updating public taxonomic data and using correct sequence similarity thresholds is emphasised.