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 mushroom collectors. Their distinguishing characteristics include usually brightly coloured caps, a white to dark yellow spore print, brittle, attached gills, an absence of latex, and absence of partial veil or volva tissue on the stem. Microscopically, the genus is characterised by the amyloid ornamented spores and flesh (trama) composed of spherocysts. Members of the related genus Lactarius have similar characteristics but emit a milky latex when their gills are broken. The genus was described by Christian Hendrik Persoon in 1796.
Taxonomy
Christian Hendrik Persoon first circumscribed the genus Russula in his 1796 work Observationes Mycologicae, and considered the defining characteristics to be the fleshy fruit bodies, depressed cap, and equal gills.[9] He reduced it to the rank of tribe in the genus Agaricus in 1801. Elias Fries similarly regarded Russula as a tribe of Agaricus in his influential Systema Mycologicum (1821), but later (1825) raised it to the rank of genus in the Systema Orbis Vegetabilis. Around the same time, Samuel Frederick Gray also recognized Russula as a genus in his 1821 work The Natural Arrangement of British Plants.[10]
The name Russula is derived from the Latin word russus, meaning "red".[11]
Identification
"If we know of any one, who in the pride of intellect spurned all mental tasks as mere play, we would tame him by insisting on his mastering, classifying and explaining the synonyms of the genus Russula."
Like the genus Lactarius, russulas have a distinctive flesh consistency, which is also reflected in the appearance of the gills and stipe, and normally makes them immediately recognizable. They have no trace of a veil (no ring, or veil remnants on the cap). The gills are brittle except in a few cases, and cannot be bent parallel with the cap without breaking. Hence the genus Russula is sometimes known colloquially as "brittle gills".[12] They have splitting gills and do not exude a milky substance at cut surfaces, contrary to the genus Lactarius. Presence of large spherical cells, 'sphaerocysts', in the stipe is an important characteristic feature to distinguish the members of Russulaceae from other mushrooms. In Russula, the stipe breaks like the flesh of an apple, while in most other families it only breaks into fibres.[13] The spore powder varies from white to cream, or even orange.
While it is relatively easy to identify a sample mushroom as belonging to this genus, it is a significant challenge to distinguish member species of Russula. This task often requires microscopic characteristics, and subtle subjective distinctions, such as the difference between a mild to bitter and a mild to acrid flavor. Moreover, the exact phylogenetic relationships of these mushrooms have yet to be resolved in the professional mycological community, and may ultimately depend on DNA sequencing analysis.
The following characteristics are often important in identifying individual species:
the exact colour of the spore powder (white/cream/ochre),
the taste (mild/bitter/acrid),
colour changes in the flesh,
the distance from the centre to which the cap skin can be pulled off: (peeling percentage).
cap colour (but this is often very variable within one species),
reaction of the flesh to ferrous sulphate (FeSO4), formalin, alkalis, and other chemicals,
ornamentation of the spores, and
other microscopic characteristics, such as the appearance of the cystidia in various mounting reagents.
Despite the difficulty in positively identifying collected specimens, the possibility to spot the toxic species by their acrid taste makes some of the mild species, such as R. cyanoxantha and R. vesca, popular edible mushrooms. Russula is mostly free of deadly poisonous species, and mild-tasting ones are all edible.[14][failed verification]
Ecology
All Russula species are ectomycorrhizal symbionts with higher plants and trees, and the genus has a collectively diverse host range.[15] Some species are cosmopolitan and capable of forming associations with one or more hosts in a range of habitats, while others are more constrained in either host or habitat or both.[16] The mycoheterotrophic plant Monotropa uniflora associates with a small range of fungal hosts, all of them members of Russulaceae, including 18 species of Russula.[17]
Humans collect several species of Russula for food. There is a cultural divide toward interpretation of Russula edibility. In general, North American field guides tend to list mostly non-edible species and advise caution when consuming any member of the genus. In contrast, European field guides have a more favorable opinion and list more edible species.[12]
In Madagascar, species collected from introduced eucalypt forests include Russula madecassense, Russula prolifica, and several other species of minor importance, including some that have not yet been officially described.[26]Russula is the most commonly consumed and economically important mushroom genus in Madagascar, particularly Russula prolifica and Russula edulis. This and other edible Russula are typically stripped of their cap cuticle before selling to make them more similar in appearance to the Agaricus bisporus.[27] In Tanzania, Russula cellulata and Russula ciliata are sometimes used as food.[28]
The main pattern of toxicity seen among Russula species to date has been gastrointestinal symptoms in those with a spicy (acrid) taste when eaten raw or undercooked; many of these are red-capped species such as R. emetica, R. sardonia and R. nobilis. The Asian species Russula subnigricans has been the cause of several fatal cases of rhabdomyolysis in Japan.[34] Several active agents have been isolated from the species, including russuphelin A[35] and cycloprop-2-ene carboxylic acid.[36]
^Massee GE. (1898). "Fungi exotici, I". Bulletin of Miscellaneous Informations of the Royal Botanical Gardens Kew. 1898 (138): 113–136. doi:10.2307/4115483. JSTOR4115483.
^ abLebel T, Tonkin JE (2007). "Australasian species of Macowanites are sequestrate species of Russula (Russulaceae, Basidiomycota)". Australian Systematic Botany. 20 (4): 355–381. doi:10.1071/SB07007.
^Schröter J. (1889). Kryptogamen-Flora von Schlesien. Vol. 3-1(5). Lehre, Germany: Cramer. p. 549.
^Persoon CH. (1796). Observationes mycologicae (in Latin). Leipzig, Germany: Apud Petrum Phillippum Wolf. p. 100. Archived from the original on 2014-12-05. Retrieved 2014-11-27. Pileus carnorufus, utplurimum depressus; Lamellae longitudine aequales.
^Roberts C, Ceska O, Kroeger P, Kendrick BW (2004). "Macrofungi from six habitats over five years in Clayoquot Sound, Vancouver Island". Canadian Journal of Botany. 82 (10): 1518–1538. doi:10.1139/B04-114.
^Yang S, Pfister DH (2006). "Monotropa uniflora plants of eastern Massachusetts form mycorrhizae with a diversity of russulacean fungi". Mycologia. 98 (4): 535–540. doi:10.3852/mycologia.98.4.535. PMID17139846. S2CID39886589.
^Maser C, Maser Z, Trappe JM (1985). "Food habits of the northern flying squirrel (Glaucomys sabrinus) in Oregon". Canadian Journal of Zoology. 63 (4): 1084–1088. doi:10.1139/z85-162. JSTOR1938784.
^Drewnowska M, Sąpór A, Jarzyńska G, Nnorom IC, Sajwan KS, Falandysz J (2012). "Mercury in Russula mushrooms: Bioconcentration by Yellow-ocher Brittle Gills Russula ochroleuca". Journal of Environmental Science and Health, Part A. 47 (11): 1577–91. Bibcode:2012JESHA..47.1577D. doi:10.1080/10934529.2012.680420. PMID22702818. S2CID27097507.
^Wang XH, Yang ZL, Li YC, Knudsen H, Liu PG (2009). "Russula griseocarnosa sp. nov. (Russulaceae, Russulales), a commercially important edible mushroom in tropical China: mycorrhiza, phylogenetic position, and taxonomy". Nova Hedwigia. 88 (1–2): 269–82. doi:10.1127/0029-5035/2009/0088-0269.
^Matsuura M, Saikawa Y, Inui K, Nakae K, Igarashi M, Hashimoto K, Nakata M (2009). "Identification of the toxic trigger in mushroom poisoning". Nature Chemical Biology. 5 (7): 465–7. doi:10.1038/nchembio.179. PMID19465932.
^Zhang G, Sun, J, Wang H, Ng TB. (2010). "First isolation and characterization of a novel lectin with potent antitumor activity from a Russula mushroom". Phytomedicine. 17 (10): 775–781. doi:10.1016/j.phymed.2010.02.001. PMID20378319.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^Vidari G, Che Z, Garlaschelli L (1998). "New nardosinane and aristolane sesquiterpenes from the fruiting bodies of Russula lepida". Tetrahedron Letters. 39 (33): 6073–6076. doi:10.1016/S0040-4039(98)01251-9.
^Tan JW, Xu JB, Dong ZJ, Luo DQ, Liu JK (2004). "Nigricanin, the first ellagic acid derived metabolite from the basidiomycete Russula nigricans". Helvetica Chimica Acta. 87 (4): 1025–1029. doi:10.1002/hlca.200490074.
^Lebel T, Trappe JM (2000). "Type Studies of Sequestrate Russulales. I. Generic Type Species". Mycologia. 92 (6): 1188–1205. doi:10.2307/3761486. JSTOR3761486.
^Trierveiler-Pereira L, Smith ME, Trappe JM, Nouhra E (2014). "Sequestrate fungi from Patagonian Nothofagus forests: Cystangium (Russulaceae, Basidiomycota)". Mycologia. 107 (1): 90–103. doi:10.3852/13-302. hdl:11336/12605. PMID25232070. S2CID9078246.
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