Contrasting patterns in the milk cap genera Lactarius and Lactifluus

Bobby Sulistyo
Bobby.Sulistyo@ugent.be

Promotor : Mieke Verbeken

Lactarius and Lactifluus (milk caps) are two closely related genera of fungi belonging in the Russulaceae family. Though phylogenetically distinct and molecularly well-supported, both genera are superficially similar and no synapomorphic characteristics have been found to consistently separate them. Several trends exist to somewhat separate the genera though they are non-exclusive, such as zonate and viscose caps in many Lactarius while velutinous and veiled caps are found in Lactifluus. Likewise, hymenophoral trama composing of sphaerocytes and thick-walled elements in the pileipellis and stipitipellis are mostly found in Lactifluus. One key and interesting difference is distribution, as Lactifluus is primarily distributed in the tropics while Lactarius in the subtropics. As such, their biogeographical history is an interesting area of study as it may reveal undiscovered aspect of both genera. My project will mainly focus on comparing the biogeographical history of both genera. Biogeographical analyses require balanced and thorough global sampling, and there is a general lack of sampling from Indonesia, an interesting region composed of both Indomalay and Australasia region, as well as the transitionary Wallacea region. Therefore, another focus of my project is to discover the diversity of milk caps in Indonesia.

There is currently up to 270 described species of Lactifluus, but the total number of species is roughly estimated to be around 530. Amongst all biogeographical regions, the diversity of Lactifluus is most understood in Europe. In recent year our research group has focused on Africa, the Neotropics and certain regions in SE Asia (e;g. Thailand), that increased the sampling effort significantly and resulted in the description of many new species, although missing data still are a fact in these regions (De Crop, 2016). Lactarius has approximately 420 described species and the species accumulation curve has not seemed to have reached the plateau as of the writing of this proposal. Likewise, Lactarius diversity in Europe is generally more understood than in the tropics. Metabarcoding studies in tropical Asia revealed that only a fraction of the Lactifluus sequences can be matched to known species, and that there are possibly three new lineages (De Crop et al., 2021). Similarly, subgeneric divisions in Lactarius has largely been based on European species and tropical taxa might represent new lineages as well as new subgenera (Nuytinck et al., 2020). More conclusive sampling in tropical Asia may reveal new species and lineages, as well as connects metabarcodes to morphospecies, which ultimately benefits further studies of the genera, especially in character evolution and biogeography as balanced global sampling is necessary.