Lactarius

Lactarius is a genus of mushroom-producing, ectomycorrhizal fungi, containing several edible species. The species of the genus, commonly known as milk-caps, are characterized by the milky fluid ('latex') they exude when cut or damaged. Like the closely related genus Russula, their flesh has a distinctive brittle consistency. It is a large genus with roughly 450 known species, mainly distributed in the Northern hemisphere. Recently, the genus Lactifluus has been separated from Lactarius based on molecular phylogenetic evidence. The genus Lactarius was described by Christian Hendrik Persoon in 1797 with L. piperatus as the original type species. In 2011, L. torminosus was accepted as the new type of the genus after the splitting-off of Lactifluus as separate genus. The name 'Lactarius' is derived from the Latin lac, 'milk'. Molecular phylogenetics uncovered that, while macromorphologically well-defined, milk-caps were in fact a paraphyletic genus; as a consequence, the genera Lactifluus was split from Lactarius, and the species L. furcatus was moved to the new genus Multifurca, together with some former Russula species. Multifurca also represents the likely sister group of Lactarius (see phylogeny, right). In the course of these taxonomical rearrangements, the name Lactarius was conserved for the genus with the new type species Lactarius torminosus; this way, the name Lactarius could be retained for the bigger genus with many well-known temperate species, while the name Lactifluus has to be applied only to a smaller number of species, containing mainly tropical, but also some temperate milk-caps such as Lactifluus volemus and Lf. vellereus. Phylogenetic analyses have also revealed that Lactarius, in the strict sense, contains some species with closed (angiocarpous) fruitbodies, e.g. L. angiocarpus described from Zambia. The angiocarpous genera Arcangeliella and Zelleromyces are phylogenetically part of Lactarius. Systematics within Lactarius is a subject of ongoing research. Three subgenera are currently accepted and supported by molecular phylogenetics: Some more species, all tropical, do not seem to fall into these subgenera and occupy more basal positions within Lactarius. This includes for example L. chromospermus from tropical Africa with an odd brown spore color. Currently, around 600 Lactarius species are described, but roughly one fourth or 150 of these are believed to belong to Lactifluus, while the angiocarpous genera Arcangeliella and Zelleromyces have not yet been synonymized with Lactarius. It is estimated that a significant number of Lactarius species remain to be described.