Russulaceae
Template:Short description Template:Featured article Template:Automatic taxobox
The Russulaceae are a diverse family of fungi in the order Russulales, with roughly 1,900 known species and a worldwide distribution. They comprise the brittlegills and the milk-caps, well-known mushroom-forming fungi that include some edible species. These gilled mushrooms are characterised by the brittle flesh of their fruitbodies.
In addition to these typical agaricoid forms, the family contains species with fruitbodies that are laterally striped (pleurotoid), closed (secotioid or gasteroid), or crust-like (corticioid). Molecular phylogenetics has demonstrated close affinities between species with very different fruitbody types and has discovered new, distinct lineages.
An important group of root-symbiotic ectomycorrhizal fungi in forests and shrublands around the world includes Lactifluus, Multifurca, Russula, and Lactarius. The crust-forming genera Boidinia, Gloeopeniophorella, and Pseudoxenasma, all wood-decay fungi, have basal positions in the family.
TaxonomyEdit
The family Russulaceae was first validly named in 1907 by Dutch botanist Johannes Paulus Lotsy,<ref name="urlMycoBank: Russulaceae"/> who included three genera: Russula, Lactarius, and Russulina (now considered a synonym of Russula). He emphasised features such as the granular flesh, thick gills, spiny spores, and milky hyphae and rounded cells (sphaerocytes).<ref name="Lotsy 1907"/> A prior usage of "Russulariées" by French mycologist Ernst Roze in 1876<ref name="Roze 1876"/> is not considered a valid publication, since the proper Latin termination for the family rank specified in article 18.4 of the nomenclature code was not used.<ref name="urlMycoBank: Russulaceae"/><ref name="MelbourneCodeArt18"/>
Synonyms of Russulaceae include: Ernst Albert Gäumann's Lactariaceae (1926), Fernand Moreau's Asterosporaceae (1953),<ref name="Pegler 1979"/> and David Pegler and Thomas Young's Elasmomycetaceae (1979). The latter family was proposed to contain species with statismosporic (non-forcibly discharged) and symmetric spores, including the gasteroid genera Elasmomyces, Gymnomyces, Martellia, and Zelleromyces. Calonge and Martín reduced the Elasmomycetaceae to synonymy with the Russulaceae when molecular analysis confirmed the close genetic relationship between the gasteroid and agaricoid genera.<ref name="Calonge 2000"/>
Placement of the familyEdit
Historically, the gilled mushrooms of the family Russulaceae were classified with other gilled species in the order Agaricales,<ref name=Singer1986/> but microscopical studies of spore and fruitbody flesh features raised the possibility that they were more closely related with certain "lower fungi" presenting nongilled, crust-like fruitbodies.<ref name="Pegler 1979"/><ref name=Donk1971/><ref name=Oberwinkler1977/> The use of molecular phylogenetics confirmed that these morphologically diverse fungi form a distinct lineage, first termed the "russuloid clade"<ref name=Larsson2003/><ref name=Hibbett2001/> and today classified as order Russulales in the class Agaricomycetes.<ref name=Hibbett2007/> The family's sister group within the order appears to be the crust-like Gloeocystidiellaceae.<ref name=Larsson2007/>
Internal systematicsEdit
A 2008 molecular phylogenetic study clarified the relationships among the mushroom-forming species of the family.<ref name=Buyck2008/> The authors demonstrated the existence of four distinct lineages of gilled mushrooms, which led to the description of Multifurca as a new genus separated from Russula<ref name=Buyck2008/> and the segregation of Lactifluus from Lactarius.<ref name=Buyck2010/><ref name=verbeken2013/>
Genera with closed fruitbodies within the family are form taxa instead of natural groups: Arcangeliella, Gastrolactarius, and Zelleromyces are phylogenetically part of Lactarius, while Cystangium, Elasmomyces, Gymnomyces, Macowanites, and Martellia belong to Russula.<ref name="Calonge 2000"/><ref name=Buyck2010/> Nevertheless, some of these genus names are still in use, as many of the concerned species have not yet formally been synonymised with Lactarius or Russula.<ref name=kirk2014/>
The crust-like genera Boidinia, Gloeopeniophorella, and Pseudoxenasma, formerly placed in the Corticiaceae or Gloeocystidiellaceae, are now classified in the Russulaceae and basal to the clade of mushroom-forming species described above.<ref name=Larsson2007/><ref name=kirk2014/> Studies have so far failed to clearly circumscribe and place these genera within the family.<ref name=Larsson2003/><ref name=Larsson2007/><ref name="Miller2006"/> Boidinia in its current extent is polyphyletic, with some species not falling into the Russulaceae.<ref name=Larsson2003/>
Species diversityEdit
Altogether, the Russulaceae comprise around 1,900 accepted species.<ref name=kirk2014/> Russula is by far the largest genus with c. 1,100 species, Lactarius has c. 550, Lactifluus c. 120, Boidinia 13, Multifurca 6, Gloeopeniophorella 6, and Pseudoxenasma 1 species.<ref name=kirk2014/><ref name="Lebel2013"/> Closed-fruitbody species not yet synonymised with Lactarius or Russula (see above) account for some 150 species.<ref name=kirk2014/>
New species in the Russulaceae continue to be described from various regions, such as the US,<ref name=Arora2014/> Guyana,<ref name=Miller2013/> Brazil,<ref name=Sa2013a/> Patagonia,<ref name="Trierveiler-Pereira2014"/> Togo,<ref name=Maba2013/> Sri Lanka,<ref name="verbeken2014"/> or Thailand.<ref name="verbeken2014"/> It has been estimated that the real number of Russula species in North America alone (currently around 400 described) might be as high as 2000.<ref name=Vellinga2013/> Cryptic species may increase true diversity: some morphologically well-defined species, especially in Lactifluus, have been shown to actually encompass several phylogenetic species.<ref name=VandePutte2010/><ref name=DeCrop2014/><ref name=ugent-lactifluus/>
DescriptionEdit
Macroscopic characteristicsEdit
Template:Multiple image Three major types of fruitbodies occur in the Russulaceae: agaricoid and pleurotoid forms with a cap, gills, and a stipe; forms with closed (gasteroid) or partially closed (secotioid) fruitbodies, and corticioid, crust-like forms.
The agaricoid species in Lactarius, Lactifluus, Multifurca, and Russula are readily distinguished from other gilled mushrooms by the consistency of their flesh, which is granular, brittle and breaks easily, somewhat like a piece of chalk.<ref name="Lotsy 1907"/><ref name="urlRussulalesNmorphology"/> Russulaceae never have a volva,<ref name="urlRussulalesNmorphology"/> but a partial veil can be found in some tropical species.<ref name="Heim1938"/><ref name="Singer1983"/> Gills are adnate to decurrent, and the colour of the spore print ranges from white to ochre or orange<ref name="Buyck2008"/><ref name="Courtecuisse2013"/> (with the brown-spored Lactarius chromospermus as an exception).<ref name=Buyck1995/>
Caps can be dull to very colourful, the latter especially in Russula;<ref name="Courtecuisse2013"/> their size ranges from 17 mm diameter or less in Russula campinensis<ref name="Henkel2000"/> to Template:Convert in Lactifluus vellereus.<ref name="Courtecuisse2013"/> Concentrically ringed (zonate) caps occur in all Multifurca<ref name="Buyck2008"/> and several Lactarius species.<ref name="Courtecuisse2013"/> Laterally striped (pleurotoid) fruitbodies exist in some, mainly tropical Lactifluus and Russula species.<ref name="Henkel2000"/><ref name="Buyck1999"/><ref name="Wang2012"/><ref name="Morozova 2013"/> Taste is a distinguishing characteristic in many species, from mild to very acrid.<ref name="Courtecuisse2013"/> A conspicuous feature of the "milk-caps" in Lactarius, Lactifluus, and Multifurca furcata is the latex or "milk" their fruitbodies exude when bruised.<ref name="Buyck2008"/><ref name="urlRussulalesNmorphology"/>
The secotioid and gasteroid species in Lactarius and Russula are derived from agaricoid forms.<ref name="Buyck2008"/><ref name="Thiers1984"/> Secotioid species still have a stipe but the cap does not open fully, while in gasteroid species, fruitbodies are completely closed and the stipe is reduced; in both cases, the spore-bearing structure is made up of convoluted gills that are more or less crowded and anastomosed.<ref name="Thiers1984"/> These closed-fruitbody species represent a continuum of secotioid to gasteroid, above-ground to below-ground fruitbodies, with spores forcibly discharged or not.<ref name="verbeken2014"/><ref name="Thiers1984"/><ref name="Desjardin2003"/> Secotioid or gasteroid Lactarius exude latex just like their agaricoid relatives.<ref name="Calonge 2000"/><ref name="verbeken2014"/><ref name="Desjardin2003"/>
The corticioid species of Boidinia, Gloeopeniophorella, and Pseudoxenasma develop crust-like fruitbodies with a smooth, porous, or flaky surface and grow on tree logs or dead branches.<ref name=Larsson2003/><ref name="Maekawa1994"/><ref name="Hjortstam1976"/><ref name="Hjortstam2007"/>
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| *These species belong phylogenetically to Lactarius. |
Microscopic characteristicsEdit
All Russulaceae, including the corticioid species, are characterised by spherical to elliptic basidiospores with a faint to very distinct (e.g. warty, spiny, or crested) ornamentation that stains bluish-black with Melzer's reagent (an amyloid stain reaction).<ref name="Larsson2003"/><ref name="urlRussulalesNmorphology"/> Basidia (spore-bearing cells) are usually club-shaped and four-spored.<ref name="Cannon 2007"/> Russulaceae species do not have clamp connections.<ref name="Ammirati 1985"/>
Characteristic cells with an oily content (gloeocystidia) are found in the hymenium. In Russulaceae, these show a positive colour reaction when treated with sulfoaldehydes (sulfovanillin is mostly used).<ref name="Larsson2003"/><ref name="urlRussulalesNmorphology"/> They are also present in the hyphal sheath of ectomycorrhizal roots colonised by Russulaceae.<ref name="Miller2006"/>
The feature responsible for the brittle fruitbody structure in the mushroom-forming species are globular cells, called sphaerocytes or sphaerocysts, that compose the flesh (trama) alongside the usual hyphae.<ref name="urlRussulalesNmorphology"/> Sometimes, these cells are clustered, and the position and arrangement of these clusters differs among genera.<ref name="urlRussulalesNmorphology"/>
Another particular trama cell type are lactiferous hyphae (also lactifers). These are hyphae carrying the "milk" or "latex" exuded by the milk-caps; they react positively with sulfoaldehydes, form an abundantly branched system in the trama and end as pseudocystidia in the hymenium.<ref name="urlRussulalesNmorphology"/> In general, only Lactarius, Lactifluus and Multifurca furcata possess lactifers.<ref name="Buyck2008"/> In Russula, similar hyphae can sometimes be observed in the trama, but these are not as abundantly branched as real lactifers and do not extend into the hymenium as pseudocystidia.<ref name="urlRussulalesNmorphology"/> This traditional distinction line between the "milk-caps" and Russula is however less evident in some tropical species presenting intermediate states.<ref name="Buyck1999"/>
Genera distinctionEdit
Some characteristics of the mushroom-forming genera (marked with * below) can be less obvious or absent in tropical species.<ref name="Buyck2008"/><ref name="Buyck1999"/> Distinguishing between Lactarius and Lactifluus based on morphology alone is quite difficult, as clear synapomorphies for both genera have yet to be identified.<ref name="verbeken2013"/> Most field guides treat the two genera together, often because Lactifluus is not yet recognised as a separate genus.<ref name="Courtecuisse2013"/><ref name="Bessette1996"/>
- Boidinia: corticioid; loose texture; surface smooth, with pores, or flaky; spores spherical with spiny to warty ornamentation.<ref name=Larsson2003/><ref name="Maekawa1994"/> Note that the genus is polyphyletic and needs to be redefined.<ref name=Larsson2003/>
- Gloeopeniophorella: corticioid; surface almost smooth; hyphae without clamp connections; thick-walled cystidia (metuloids) and gloeocystidia present; spores with wrinkled (rugose) ornamentation.<ref name="Hjortstam2007"/>
- Lactarius: agaricoid or gasteroid; exuding latex*; caps sometimes zonate, viscose or glutinate, but never annulate; rarely thick-walled cells in cuticles of the cap (pileipellis) and the stipe (stipitipellis) and sphaerocytes in the gills.<ref name="Buyck2008"/><ref name="verbeken2013"/>
- Lactifluus: agaricoid or pleurotoid; exuding latex*; caps never zonate, viscose or glutinate, but sometimes annulate; thick-walled cells in cap and stipe cuticles; often sphaerocytes in the gill trama.<ref name="Buyck2008"/><ref name="verbeken2013"/>
- Multifurca: agaricoid; caps zonate (also visible in cut through trama); gills regularly forked; only M. furcata exuding latex; spore print orange; spores very small; microscopical trama and hymenium features very variable.<ref name="Buyck2008"/>
- Pseudoxenasma: corticioid; wax-like texture; gloeocystidia with spherical apical appendices; basidia developing laterally on hyphae (pleurobasidia); spores broadly ellipsoid to roughly spherical, with warty ornamentation.<ref name="Hjortstam1976"/>
- Russula: agaricoid, gasteroid or pleurotoid; never exuding latex; caps often brightly coloured with stipe and gills much paler; caps not zonate*; spore print white, cream, ochre, or orange; no true lactiferous hyphae*; sphaerocytes abundant in gill, cap, and stipe trama.<ref name="Buyck2008"/><ref name="urlRussulalesNmorphology"/>
DistributionEdit
The Russulaceae as a whole have a worldwide distribution, but patterns differ among genera. Russula is the most widespread, found in North,<ref name=Earle1902a/><ref name=Earle1902b/> Central<ref name="Gómez1996"/><ref name="Buyck2002"/> and South America,<ref name="Singer1983"/><ref name="Sa2013b"/> Europe,<ref name="Courtecuisse2013"/> temperate<ref name=Guo2014/><ref name="Gorbunova2014"/> and tropical Asia,<ref name="Lee1997"/><ref name="Natarajan2005"/> Africa,<ref name=Verbeken2002/> and Australasia.<ref name="Buyck1999"/><ref name="Bougher1996"/><ref name="McNabb1973"/> It is the only Russulaceae genus that occurs in the Nothofagus zone of temperate South America.<ref name="Singer1953"/>
Lactarius is mainly known from the north temperate zone, but some species also occur in tropical Asia and Africa.<ref name="verbeken2013"/> Lactifluus has a more tropical distribution than Lactarius, with most species known from tropical Africa, Asia, South America, and Australasia, but some also occurring in the north temperate zone.<ref name="verbeken2013"/> Multifurca is the rarest among the four mushroom genera, known only from some punctual records in North and Central America, Asia, and Australasia.<ref name=Buyck2008/><ref name="Lebel2013"/>
Species of Lactarius, Lactifluus, and Russula have repeatedly been introduced with trees outside their native range: An overview article lists introductions in Chile, Argentina, Uruguay, Brazil, the US, Great Britain, the Faroe Islands, South Africa, China, Thailand, and New Zealand.<ref name="Vellinga2009"/>
Among the corticioid genera, Pseudoxenasma is only known from Europe.<ref name="urlGBIFPseudoxenasma"/> In contrast, Boidinia species have been found in Europe,<ref name="Bernicchia2010"/> Taiwan,<ref name="Wu1996"/> and Japan,<ref name="Maekawa1994"/> and Gloeopeniophorella species in North America,<ref name="Ginns1994"/> South America,<ref name="Hjortstam2007"/><ref name="Boidin1997"/> Europe,<ref name="Eriksson1975"/> West Africa,<ref name="Boidin1997"/> Taiwan,<ref name="Wu1996"/> Australia,<ref name="Hjortstam2007"/> and New Zealand.<ref name="Hjortstam2007"/>
EcologyEdit
Ectomycorrhizal symbiosisEdit
The genera Lactarius, Lactifluus, Multifurca and Russula form a mutualistic ectomycorrhizal root symbiosis with trees and shrubs, exchanging mineral nutrients for photosynthetic sugar. They are one of several fungal lineages that have evolved such a lifestyle and are sometimes referred to as the "/russula-lactarius" clade in the scientific literature.<ref name="urlECMlineages"/> Worldwide, they are one of the most frequently encountered lineages on ectomycorrhizal roots.<ref name="Tedersoo2010"/> While some tropical species were initially believed to be parasitic, the observation that species fruiting on tree trunks do form ectomycorrhiza in tropical Guyana supports the view of an exclusively symbiotic lineage.<ref name="Henkel2000"/>
Associations are known with several plant families. In the Northern Hemisphere, these are essentially the well-known ectomycorrhizal trees and shrubs in the Betulaceae, Fagaceae, Pinaceae and Salicaceae,<ref name="Courtecuisse2013"/><ref name="Bessette1996"/> but in arctic and alpine habitats, Russulaceae also associate with Bistorta vivipara (Polygonaceae),<ref name="Gardes1996"/> Kobresia (Cyperaceae),<ref name="Gao2010"/> and Dryas octopetala (Rosaceae),<ref name="Harrington2002"/> ectomycorrhizal plants untypic in their respective families. In the tropics, known plant partners include Dipterocarpaceae,<ref name="Natarajan2005"/><ref name=Ba2011/> Fabaceae,<ref name="Henkel2000"/><ref name=Ba2011/> Nyctaginaceae,<ref name="Haug2005"/><ref name="Tedersoo2009"/> Phyllanthaceae,<ref name=Ba2011/> Polygonaceae (Coccoloba),<ref name="Tedersoo2009"/> Sarcolaenaceae,<ref name=Ducousso2008/> and the gymnosperm Gnetum gnemon,<ref name="Tedersoo2012"/> and in the Southern Hemisphere, Nothofagaceae,<ref name="McNabb1973"/><ref name="Singer1953"/><ref name="McNabb1971"/> Myrtaceae (Eucalyptus<ref name="Bougher1996"/> and Leptospermum),<ref name="McNabb1973"/><ref name="McNabb1971"/> and Rhamnaceae (Pomaderris).<ref name="Tedersoo2008"/> Some Russulaceae are quite specialised in their ectomycorrhizal symbiosis, such as Lactarius and Russula species that only grow with Cistus shrubs in the Mediterranean basin.<ref name=Comandini2006/>
The different plant partners are reflected in the wide variety of habitats worldwide.<ref name="urlRussulalesNhabitats"/> Ectomycorrhizal Russulaceae have been observed in arctic and alpine tundra,<ref name="Gardes1996"/> boreal and alpine forest,<ref name=Guo2014/><ref name="Toljander2006"/> north temperate forest,<ref name="Courtecuisse2013"/><ref name="Bessette1996"/> mires,<ref name="Thormann2007"/> mediterranean forests and scrub (maquis),<ref name=Comandini2006/><ref name="Richard2005"/> miombo woodland,<ref name=Verbeken2002/> tropical lowland rainforest,<ref name="Natarajan2005"/><ref name="Tedersoo2009"/> tropical cloud forest,<ref name=Halling2002/> tropical dry forest,<ref name="Phosri2012"/> Australian eucalypt woodlands,<ref name="Miller1986"/> and south temperate forests.<ref name="Singer1953"/><ref name="McNabb1971"/><ref name="Tedersoo2008"/> Where they are introduced, they typically grow in plantations of their native host species, e.g. with pine in South Africa,<ref name="vanderWesthuizen1987"/> Eucalyptus in Thailand,<ref name="Chalermpongse1995"/> or birch in New Zealand.<ref name="McNabb1971"/>
Other types of mycorrhizaEdit
Some of the ectomycorrhizal Russulaceae are also involved in other types of root symbioses with plants.
A mutualistic association similar to ectomycorrhiza but with some hyphae penetrating into the plant root cells, termed arbutoid mycorrhiza,<ref name="SmithRead2008"/> is formed by Russulaceae with shrubs of the genera Arbutus<ref name="Richard2005"/> and Arctostaphylos,<ref name="Mühlmann2006"/> both in subfamily Arbutoideae of the Ericaceae.<ref name="Richard2005"/><ref name="Mühlmann2006"/>
Some Russulaceae are associated with myco-heterotrophic plants of the Ericaceae subfamily Monotropoideae, forming monotropoid mycorrhiza.<ref name="Cullings1996"/><ref name="Bidartondo2005"/> This is an epiparasitic relationship, where the heterotrophic plant ultimately derives its carbon from the primary, ectomycorrhizal plant partner of the fungus.<ref name="Bidartondo2005"/> The association is often very specific, with the heterotrophic plants only associating with selected fungus partners, including Russulaceae.<ref name="Cullings1996"/><ref name="Yang2006"/>
Russulaceae are also an important group of orchid mycorrhizal fungi.<ref name="Dearnaley2007"/> This symbiosis is mutualistic in the case of green orchids,<ref name="SmithRead2008"/> but a partly or fully epiparasitic relationship in the case of myco-heterotrophic<ref name="Taylor2004"/><ref name="Roy2009"/> and mixotrophic<ref name="Girlanda2005"/> orchids, respectively. In some cases, the association with Russulaceae is, as in monotropoid mycorrhiza, very specific: the Mediterranean orchid Limodorum abortivum predominantly associates with Russula delica and closely related species;<ref name="Girlanda2005"/> in Corallorhiza maculata, different genotypes of the same species have distinct Russula partners.<ref name="Taylor2004"/>
Wood decay speciesEdit
The corticioid species in Boidinia, Gloeopeniophorella, and Pseudoxenasma are saprotrophic, wood-degrading fungi that develop on dead wood.<ref name=Larsson2003/> Their early-branching positions in the phylogeny suggests this has been the ancestral trophic mode of the Russulaceae, and that the mycorrhizal lifestyle (see above) evolved later.<ref name=Larsson2003/> The saprotrophic nature of these species has been questioned, based on the observation that other inconspicuous, crust-forming fungi are ectomycorrhizal;<ref name="Miller2006"/> a subsequent author reaffirms nevertheless that "[n]one of the corticioid species in the family shows any sign of mycorrhizal activity."<ref name=Larsson2007/>
Hypogeous fruitingEdit
Hypogeous fruitbodies, or fruitbodies developing below ground, occur in Lactarius and Russula and have previously been considered as distinct genera (see Systematics and taxonomy: Internal systematics). As such species are especially diverse in some warm and dry regions, e.g. in Spain,<ref name="Calonge 2000"/> California,<ref name="Smith2006"/> or Australia,<ref name="Bougher1996"/> below-ground fruiting has been interpreted as an adaptation to drought.<ref name="Thiers1984"/> However, hypogeous Russulaceae are also known from cold temperate regions<ref name="Trierveiler-Pereira2014"/><ref name="Nuytinck2003"/> and tropical rainforest.<ref name="verbeken2014"/> The fact that hypogeous species in the Russulaceae do not form their own lineages but are scattered in Russula or Lactarius shows that this type of fruiting evolved several times.<ref name="verbeken2014"/> It is believed that these changes are evolutionarily quite recent.<ref name="verbeken2014"/>
ParasitesEdit
_Singer_171045_crop.jpg){kind=link}
Russulaceae fruitbodies are subject to parasitisation by other fungi. The genus Asterophora develops on old fruitbodies of the mushroom species in the family,<ref name="Bessette1996"/> as does Dendrocollybia racemosa on at least Russula crassotunicata.<ref name=Machnicki2006/> Fruitbodies of Lactifluus or Russula species otherwise hot-tasting and unpalatable are regarded as choice edibles in North America when infected by the "lobster mushroom" Hypomyces lactifluorum.<ref name="Bessette1996"/> Heterotrophic plants, including orchids or monotropoids, also parasitise ectomycorrhizal Russulaceae and their plant partners – see above, Other types of mycorrhiza.
Threats and conservationEdit
As with most fungi,<ref name="urlFungalRedList"/> little information is available on the threat of extinction for Russulaceae species, and they have not been assessed in the International Union for the Conservation of Nature's Red List.<ref name="iucn-redlist"/> However, national lists contain some species of Lactarius, Lactifluus and Russula, indicating that they have small populations and are endangered, e.g. in Great Britain,<ref name="Evans2006"/> Switzerland,<ref name="Senn-Irlet2007"/> the Czech Republic,<ref name="Holec2006"/> and New Zealand.<ref name="urlNationallyCriticalNZ"/>
Although data on Russulaceae themselves are scarce, more is known about the habitats they occur in, especially for the ectomycorrhizal species which depend on their host plants: Several of these habitats are affected by loss or degradation, such as peatlands,<ref name="Parkin1997"/> Mediterranean forests and scrub<ref name="Médail1999"/> or tropical African dry woodland.<ref name="Sjumpangani2009"/> Similarly, dead wood, the habitat of the corticioid Russulaceae, is rare in many exploited forests and needs special management.<ref name="Jonsson2005"/>
Recent studies have found some traditional Russulaceae species to comprise several cryptic species (see Systematics and taxonomy: Species diversity). This may imply that distribution range and population size for each of such distinct species are smaller than previously thought.<ref name="Bickford2007"/>
EdibilityEdit
Several species of Lactarius, Lactifluus and Russula are valued as excellent edible mushrooms. This is the case for example for the north temperate species Lactarius deliciosus, Lactifluus volemus, or Russula vesca, and other species are popular in other parts of the world, e.g. Lactarius indigo in Mexico, or Lactifluus edulis in tropical Africa.<ref name="urlRussulalesNedibility"/> Some species, like Russula vesca, can even be eaten raw.<ref name="Zeitlmayr 1976"/> The brittle texture of Russula fruitbodies makes them different from other mushrooms and is not appreciated by some.<ref name="Arora 1986"/>
Several species have a hot to very acrid taste and can cause gastrointestinal symptoms.<ref name="Miller & Miller 2006"/> Despite this, such species are eaten in some regions, e.g. Lactarius torminosus in Finland<ref name="Vetelainen2008"/> or Russia.<ref name="Molokhovets1992"/> Often, they are parboiled or pickled to make them palatable,<ref name="Roberts 2014"/> and sometimes, they are used as spice, for example Russula emetica in Eastern Europe.<ref name="Rogers2006"/> Some species are however truly poisonous: the East Asian and North American Russula subnigricans causes rhabdomyolysis and is potentially lethal,<ref name="Chen2014"/> and Lactarius turpis from Eurasia contains a mutagenic substance.<ref name=Suortti1983/>
Cultivation of edible Russulaceae, as in other ectomycorrhizal fungi, is challenging, since the presence of host trees is required. In spite of this difficulty, the European Lactarius deliciosus has been successfully grown in "mushroom orchards" in New Zealand.<ref name=Guerin-Laguette2014/>
ChemistryEdit
Fruitbodies of Russulaceae have been the subject of natural product research, and different classes of organic compounds have been isolated from them.
Aroma compounds are responsible for the particular odour or taste in some species, e.g. sotolon in the fenugreek-smelling Lactarius helvus,<ref name="Rapior2000"/> or the similar quabalactone III in Lactarius rubidus which causes a maple syrup-like odor in dried specimens.<ref name="Wood2012"/> Pigments have been isolated from brightly coloured species, e.g. (7-isopropenyl-4-methylazulen-1-yl)methyl stearate from the blue Lactarius indigo<ref name="Harmon1979"/> or russulaflavidin and a derivative from the yellow Russula flavida.<ref name="Fröde1995"/> Some Russula species contain pigmented pteridine derivatives called russupteridines that are not found in the milk-caps.<ref name="Gry 2014"/> Sesquiterpenes are characteristic secondary metabolites of many Russulaceae, especially milk-caps which have been quite intensively studied.<ref name="Vitari1995"/><ref name="Kobata1995"/> They are thought to be responsible for the hot taste in many species and may have deterrent, antifeeding functions in nature.<ref name="Vitari1995"/>
Other metabolites isolated from different species include dibenzonaphtyridinone alkaloids,<ref name="Vitari1995"/> prenylated phenols,<ref name="Vitari1995"/> benzofurans,<ref name="Vitari1995"/> chromenes,<ref name="Vitari1995"/> natural rubber (polyisoprene),<ref name="Tanaka1994"/> sterols,<ref name=Yue2001/> and the sugar alcohol volemitol.<ref name=Bourquelot1889/> Among toxic substances, Lactarius turpis contains the mutagenic alkaloid necatorin,<ref name=Suortti1983/> and the small compound cycloprop-2-ene carboxylic acid has been identified as the toxic agent in Russula subnigricans.<ref name="Matsuura2009"/> Some secondary metabolites showed antibiotic properties in laboratory tests.<ref name="Vitari1995"/> An ethanolic extract of Russula delica was antibacterial,<ref name="Yaltirak2009"/> and a lectin from Russula rosea showed antitumor activity.<ref name="Zhang 2010"/>