''Lactarius'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

mushroom A mushroom or toadstool is the fleshy, spore-bearing fruiting body of a fungus, typically produced above ground, on soil, or on its food source. ''Toadstool'' generally denotes one poisonous to humans. The standard for the name "mushroom" is ...

-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 my ...

fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately fr ...

, containing several

edible An edible item is any item that is safe for humans to eat. "Edible" is differentiated from "eatable" because it does not indicate how an item tastes, only whether it is fit to be eaten. Nonpoisonous items found in nature – such as some mushroo ...

species. The species of the genus, commonly known as milk-caps, are characterized by the milky fluid ("

latex Latex is an emulsion (stable dispersion) of polymer microparticles in water. Latexes are found in nature, but synthetic latexes are common as well. In nature, latex is found as a milky fluid found in 10% of all flowering plants (angiosperms ...

") they exude when cut or damaged. Like the closely related genus ''

Russula ''Russula'' is a very large genus composed of around 750 worldwide species of ectomycorrhizal mushrooms. They are typically common, fairly large, and brightly colored – making them one of the most recognizable genera among mycologists and mushr ...

'', 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 ''Lactifluus'' is one of three genera of mushroom-forming fungi containing species commonly named " milk-caps", the others being ''Lactarius'' and ''Multifurca''. It has been separated from ''Lactarius'' based on molecular phylogenetic evidence ...

'' 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 Christiaan Hendrik Persoon (1 February 1761 – 16 November 1836) was a German mycologist who made additions to Linnaeus' mushroom taxonomy. Early life Persoon was born in South Africa at the Cape of Good Hope, the third child of an i ...

in 1797 with '' L. piperatus'' as the original

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specim ...

. 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 Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through ...

'' lac'', "

milk Milk is a white liquid food produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals (including breastfed human infants) before they are able to digest solid food. Immune factors and immune-modulat ...

Placement within Russulaceae

Molecular phylogenetics 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 ...

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

paraphyletic In taxonomy, a group is paraphyletic if it consists of the group's last common ancestor and most of its descendants, excluding a few monophyletic subgroups. The group is said to be paraphyletic ''with respect to'' the excluded subgroups. In ...

genus; as a consequence, the genera ''

'' 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 ...

of ''Lactarius'' (see phylogeny, right). In the course of these taxonomical rearrangements, the name ''Lactarius'' was conserved for the genus with the new

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 descri ...

''; 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''

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, ...

'' 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 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 A veil is an article of clothing or hanging cloth that is intended to cover some part of the head or face, or an object of some significance. Veiling has a long history in European, Asian, and African societies. The practice has been prominent ...

, 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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