Lactarius Pegleri

''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 over 500 known species, mainly distributed in the Northern hemisphere. Recently, the genus ''Lactifluus'' has been separated from ''Lactarius'' based on molecular phylogenetic evidence.

Systematics and taxonomy

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".

Placement within Russulaceae

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''.

Relationships within ''Lactarius''

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:
*''Piperites'': Northern temperate region, three species in tropical Africa.
*''Russularia'': Northern temperate region and tropical Asia.
*''Plinthogalus'': Northern temperate region, tropical Africa, and tropical Asia.
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.

Description

Macromorphology

The eponymous "milk" and the brittle consistency of the flesh are the most prominent field characters of milk-cap fruitbodies. The milk or latex emerging from bruised flesh is often white or cream, but more vividly coloured in some species; it can change upon exposition or remain unchanged. Fruitbodies are small to very large, gilled, rather fleshy, without veil, often depressed or even funnel-shaped with decurrent gills. Cap surface can be glabrous, velvety or pilose, dry, sticky or viscose and is often zonate