Lactarius is agenus ofmushroom-producing,ectomycorrhizalfungi, containing severaledible species. The species of the genus,commonly known asmilk-caps, are characterized by the milky fluid ("latex") they exude when cut or damaged. Like the closely related genusRussula, their flesh has a distinctive brittle consistency. It is a large genus with over 500 known species,[1] mainly distributed in the Northern hemisphere. Recently, the genusLactifluus has been separated fromLactarius based onmolecular phylogenetic evidence.
Phylogenetic relationships ofLactarius,Lactifluus,Multifurca, andRussula according to Buyck et al. 2008.[7]
Molecular phylogenetics uncovered that, while macromorphologically well-defined, milk-caps were in fact aparaphyletic genus; as a consequence, the generaLactifluus was split fromLactarius, and the speciesL. furcatus was moved to the new genusMultifurca, together with some formerRussula species.[4][7]Multifurca also represents the likelysister group ofLactarius (see phylogeny, right). In the course of these taxonomical rearrangements, the nameLactarius was conserved for the genus with the newtype speciesLactarius torminosus; this way, the nameLactarius could be retained for the bigger genus with many well-known temperate species, while the nameLactifluus has to be applied only to a smaller number of species, containing mainly tropical, but also some temperate milk-caps such asLactifluus volemus andLf. vellereus.[4][5][6]
Arcangeliella crassa is one of the milk-caps with closed fruitbodies that are phylogenetically nested withinLactarius.
Phylogenetic analyses have also revealed thatLactarius, in the strict sense, contains some species with closed (angiocarpous) fruitbodies, e.g.L. angiocarpus described from Zambia.[8] The angiocarpous generaArcangeliella andZelleromyces are phylogenetically part ofLactarius.[8][9]
Systematics within the genusLactarius is a subject of ongoing research. Three subgenera are currently accepted and supported by molecular phylogenetics:[10]
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 additional species, all tropical, do not seem to fall into these subgenera and occupy more basal positions withinLactarius.[9] This includes for exampleL. chromospermus from tropical Africa with an odd brown spore color.[9][11]
Currently, over 600 species of the genusLactarius are recognised,[12] while the angiocarpous generaArcangeliella andZelleromyces have not yet beensynonymized withLactarius. It is estimated that a significant number ofLactarius species remain to be described.[10]
Lactarius quietus exuding cream-colored latex from gills upon cut.Spores ofLactarius alnicola showing a reticulate (net-like) ornament with an amyloid stain reaction.Lactarius indigo is one of the most strikingly coloredLactarius.
The eponymous "milk" and the brittle consistency of the flesh are the most prominent field characters of milk-capfruitbodies. 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, withoutveil, often depressed or even funnel-shaped with decurrent gills. Cap surface can be glabrous, velvety or pilose, dry, sticky or viscose and is oftenzonate. Several species have pits (scrobicules) on the cap or pileus surface. Dull colors prevail, but some more colorful species exist, e.g. the blueLactarius indigo or the orange species of sectionDeliciosi.Spore print color is white to ocher or, in some cases, pinkish. Some species have angiocarpous, i.e., closed fruitbodies.[8]
Microscopically,Lactarius species have elliptical, rarely globoid spores withamyloid ornamentation in the form of more or less prominent warts or spines, connected by ridges, like other members of the familyRussulaceae. Thetrama (flesh) contains spherical cells that cause the brittle structure. UnlikeRussula,Lactarius also have lactiferous, i.e. latex-carrying hyphae in their trama.
DistinguishingLactarius fromLactifluus based on morphology alone is difficult; there are nosynapomorphic characters known so far that define both genera unequivocally but tendencies exist:[10] zonate and viscose to glutinose caps are only found inLactarius, as well as closed (angiocarpous) and sequestrate fruitbodies. All known annulate and pleurotoid (i.e., laterally stiped) milk-caps, on the contrary, belong toLactifluus.
Characters important for identification of milk-caps (Lactarius andLactifluus) are:[13][14][15] initial colour of the latex and color change, texture of cap surface, taste (mild, peppery, or bitter) of latex and flesh, odor, and microscopical features of the spores and the cap cuticle (pileipellis). The habitat and especially the type of host tree can also be critical. While there are some easily recognizable species, other species can be quite hard to determine without microscopical examination.[15]
Lactarius is one of the most prominent genera of mushroom-forming fungi in the Northern hemisphere. It also occursnatively in Northern Africa,[13] tropical Africa,[16] tropical Asia,[9][17] Central America,[18] and Australia.[19] Its possible native distribution in South America and different parts of Australasia is unclear, as many species in those regions, poorly known, might in fact belong toLactifluus, which has a more tropical distribution thanLactarius.[20] Several species have also been introduced with their host trees outside their native range,[21] e.g. in South America,[22] Southern Africa,[16] Australia,[23] and New Zealand.[24]
Lactarius species are considered late-stage colonizers, that means, they are generally not present in early-colonizing vegetation, but establish in later phases ofsuccession.[30] However, species symbiotic with early colonizing trees, such asL. pubescens withbirch, will rather occur in early stages.[31] Several species have preferences regardingsoil pH and humidity,[13][14] which will determine the habitats in which they occur.
SeveralLactarius species are edible.L. deliciosus notably ranks among the most highly valued mushrooms in the Northern hemisphere, while opinions vary on the taste of other species, such asL. indigo orL. deterrimus. Several species are reported to be regularly collected for food in Russia, Tanzania and Hunan, China.[32] SomeLactarius are considered toxic, for exampleL. turpis, which contains the mutagenic compoundnecatorin,[33] orL. helvus. There are, however, no deadly poisonous mushrooms in the genus. Bitter or peppery species, for exampleL. torminosus, are generally not considered edible, at least raw, but are nevertheless consumed in some regions, e.g. in Finland.[34] Some small, fragrant species, such as the "candy caps", are sometimes used asflavoring.
L. deliciosus is one of the few ectomycorrhizal mushrooms that has been successfully cultivated.[35][36]
^abcEberhardt U, Verbeken A (2004). "SequestrateLactarius species from tropical Africa:L. angiocarpus sp. nov. andL. dolichocaulis comb. nov".Mycological Research.108 (Pt 9):1042–1052.doi:10.1017/S0953756204000784.PMID15506016.
^Dunstan WA, Dell B, Malajczuk. (1998). "The diversity of ectomycorrhizal fungi associated with introducedPinus spp. in the Southern Hemisphere, with particular reference to Western Australia".Mycorrhiza.8 (2):71–79.doi:10.1007/s005720050215.S2CID32374410.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^Guerin-Laguette A.; Cummings N.; Butler R.C.; Willows A.; Hesom- Williams N.; Li S.; Wang Y. (2014). "Lactarius deliciosus andPinus radiata in New Zealand: towards the development of innovative gourmet mushroom orchards".Mycorrhiza.24 (7):511–523.doi:10.1007/s00572-014-0570-y.PMID24676792.S2CID13077838.
^Anke H, Bergendorff O, Sterner O (1989). "Assays of the biological activities of guaiane sesquiterpenoids isolated from the fruit bodies of edibleLactarius species".Food and Chemical Toxicology.27 (6):393–397.doi:10.1016/0278-6915(89)90145-2.PMID2792969.
^Rapior S, Fons F, Bessière JM (2000). "The fenugreek odor ofLactarius helvus".Mycologia.92 (2):305–308.doi:10.2307/3761565.JSTOR3761565.
^Wood WF; Brandes JA; Foy BD; Morgan CG; Mann TD; DeShazer DA. (2012). "The maple syrup odour of the "candy cap" mushroom,Lactarius fragilis var.rubidus".Biochemical Systematics and Ecology.43:51–53.doi:10.1016/j.bse.2012.02.027.
^Harmon AD, Weisgraber KH, Weiss U (1979). "Preformed azulene pigments ofLactarius indigo (Schw.) Fries (Russulaceae, Basidiomycetes)".Cellular and Molecular Life Sciences.36:54–56.doi:10.1007/BF02003967.S2CID21207966.
^Doljak, B.; Stegnar, M.; Urleb, U.; Kreft, S.; Umek, A.; Ciglarič, M.; Štrukelj, B.; Popovič, T. (2001). "Screening for selective thrombin inhibitors in mushrooms".Blood Coagulation and Fibrinolysis.12 (2):123–8.doi:10.1097/00001721-200103000-00006.PMID11302474.S2CID28411589.
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