''Lactarius'' is a genus of mushroom-producing,

ectomycorrhiza An ectomycorrhiza (from Greek ἐκτός ', "outside", μύκης ', "fungus", and ῥίζα ', "root"; pl. ectomycorrhizas or ectomycorrhizae, abbreviated EcM) is a form of symbiotic relationship that occurs between a fungal symbiont, or mycobi ...

l 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 Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...

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 Lac is the resinous secretion of a number of species of lac insects, of which the most commonly cultivated is ''Kerria lacca''. Cultivation begins when a farmer gets a stick that contains eggs ready to hatch and ties it to the tree to be infes ...

'', " milk".

Placement within Russulaceae

Molecular phylogenetics uncovered that, while macromorphologically well-defined, milk-caps were in fact a

paraphyletic In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...

genus; as a consequence, the genera '' Lactifluus'' was split from ''Lactarius'', and the species '' L. furcatus'' was moved to the new genus ''

Multifurca ''Multifurca'' is a rare genus of ectomycorrhizal fungi in the family Russulaceae. It was described in 2008, after molecular phylogenetic study had shown that it forms a monophyletic lineage within the family, sister to ''Lactarius''. The genus c ...

'', together with some former ''Russula'' species. ''Multifurca'' also represents the likely

sister group In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and t ...

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 ''Lactarius torminosus'', commonly known as the woolly milkcap or the bearded milkcap, is a large agaric fungus. A common and widely distributed species, it is found in North Africa, northern Asia, Europe, and North America. It was first describ ...

''; 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 ''Lactifluus volemus'', formerly known as ''Lactarius volemus'', is a species of fungus in the family Russulaceae. It is widely distributed in the northern hemisphere, in temperate regions of Europe, North America and Asia as well as some subt ...

'' and '' Lf. vellereus''.

Relationships within ''Lactarius''

2011-07-25 Arcangeliella crassa Singer & A

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 ''Arcangeliella'' is a genus of gasteroid fungi in the family Russulaceae. Taxonomic and phylogenetic research has shown that it is very likely a synonym of ''Lactarius ''Lactarius'' is a genus of mushroom-producing, ectomycorrhizal fungi, co ...

'' and ''

Zelleromyces ''Zelleromyces'' is a genus of fungi in the family Russulaceae. It was first described by mycologists Rolf Singer and Alexander H. Smith in 1960 to contain hypogeous (underground) fungi with gasteroid fruit bodies that "bleed" latex when they are ...

'' 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

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