| Armillaria | |
|---|---|
 | |
| Armillaria mellea | |
Scientific classification | |
| Kingdom: | Fungi |
| Division: | Basidiomycota |
| Class: | Agaricomycetes |
| Order: | Agaricales |
| Family: | Physalacriaceae |
| Genus: | Armillaria (Fr.) Staude |
| Type species | |
| Armillaria mellea (Vahl)P. Kumm. | |
| Diversity | |
| c. 45 species | |
| Armillaria | |
|---|---|
| Mycological characteristics | |
 | Gills onhymenium |
 | Cap is convex |
 | Hymenium is adnate |
 | Stipe has aring |
 | Spore print is white |
 | Ecology isparasitic |
 | Edibility isedible |
Armillaria is agenus offungi that includes theA. mellea species ('honey fungus') that live on trees and woody shrubs. It includes about 10 species formerly categorized summarily asA. mellea.Armillaria sp. are long-lived and form thelargest living fungi in the world. The largest known specimen (anA. ostoyae) covers more than 3.4 square miles (8.8 km2) inOregon and is estimated to be 2,500 years old. Some species ofArmillaria displaybioluminescence.
Armillaria can be a destructiveforest pathogen. It causes"white rot" root disease. As it feeds on dead plant material, it can kill its host with little negative effect to itself.
The nameArmillaria was defined in 1821 byElias Magnus Fries, but at that time most gilled mushrooms were considered to belong to genusAgaricus andArmillaria was only a subgenus (a "tribe"). In 1857, Friedrich Staude established the independent genus.[1]
Armillaria species morphologically similar toA. mallea were not effectively distinguished until the development of "biological species" defined as intersterile groups byVeikko Hintikka in 1973.[2] Using a similar technique,Kari Korhonen showed in 1978 that the EuropeanArmillaria melleaspecies complex could be separated into five reproductively isolated species, which he named "European Biological Species" (EBS) A through E.[3] About the same time, the North AmericanA. mellea was shown to be ten different species (North American Biological Species, or NABS I through X).[4]
| Code | Taxonomic treatment | Compatibility | Known range |
|---|---|---|---|
| EBS A | Armillaria borealisMarxmüller & Korhonen (1982)[5] | Finland[6] | |
| EBS B | Armillaria cepistipesVelen. (1920)[7] | NABS III (part +rg), NABS IV (part) | Finland, Germany[6] |
| EBS C | Armillaria ostoyae(Romagn.) Herink | NABS I (part) | Finland[6] |
| EBS D | Armillaria mellea(Vahl ex Fr.) Karst | NABS VIII (part + rg) | Finland[6] |
| EBS E | Armillaria gallica(Marxmüller & Romagn.) | NABS III (part + rg) | France |
| NABS I | Armillaria ostoyae(Romagn.) Herink | EBS C (part)[6] | Vermont,[6] British Columbia, Prairie Provinces (bothboreal andsubalpine regions), Ontario, Quebec.[8] |
| NABS II | Armillaria geminaBérubé & Dessureault | Vermont,[6] Quebec.[8] | |
| NABS III | Armillaria calvescensBérubé & Dessureault | EBS B and E (part + rg)[6] | Vermont,[6]Prairie Provinces,Ontario,Quebec.[8] |
| NABS IV | EBS B (part),[6] NABS V (very low?)[7] | Vermont[6] | |
| NABS V | Armillaria sinapinaBérubé & Dessureault | EBS B (5.5%)[7] | New York (state),[6] British Columbia, Prairie Provinces, Ontario, Quebec.[8] |
| NABS VI | Armillaria mellea(Vahl.:Fries) Kummer[9] | EBS D (part)[6] | Massachusetts,[6] Quebec.[8] |
| NABS VII | Armillaria gallica(Marxmüller & Romagn.) | Vermont, Michigan,[6]British Columbia[8] | |
| NABS VIII | EBS D (part + rg)[6] | New York, Michigan.[6] | |
| NABS IX | Armillaria nabsnonaT. J. Volk & Burds. (1996) | Idaho, British Columbia.[6] | |
| NABS X | Armillaria altimontanaBrazee, B. Ortiz, Banik & D. L. Lindner (2012) | NABS V, NABS XI (both <5%)[7] | Idaho,[6] British Columbia.[8] |
| NABS XI[9] | Armillaria cepistipesVelen. (1920)[7] | EBS B (57%)[7] | British Columbia[8] |
Similar lists of biological species have been constructed by mycologists working in Japan (10 as of 1998)[10] and China (16 as of 2024).[11]
Further data from molecular diagnostic tools have removed much uncertainty for mycologists and forest pathologists. New questions remain unanswered regarding the phylogeny of North AmericanArmillaria species and their relationships to their European counterparts, particularly within the "Armillaria mellea complex". Some data suggest that North American and EuropeanA. gallica isolates are not monophyletic. Although North American and European isolates ofA. gallica may be interfertile, some North American isolates ofA. gallica are more closely related to the North American taxonA. calvescens than to European isolates ofA. gallica. The increase in genetic divergence has not necessarily barred inter-sterility between isolated populations ofA. gallica. Although the relationships among some groups in the genus seem clearer, the investigation of geographically diverse isolates has revealed that the relationship between some North American species is still unclear (Hughes et al. 2003).[12] A similar situation happens in China, where some molecular phylogenetic data appear to line up with intersterile "biological species" and others do not.[11]
Armillaria root rot occurs in theNorthwest Territories,[citation needed] and was identified onwhite spruce atPine Point onGreat Slave Lake prior to NABS findings.[citation needed]
In 1791Albrecht Wilhelm Roth described the speciesRhizomorpha fragilis for a collection which consisted entirely of rhizomorphs. The genusRhizomorpha thus became established and later thesemycelial cords were shown to belong toArmillaria mellea. According to thecode of nomenclature that means that the two genus names are synonyms and since genusArmillaria was not defined until 1857, the nameRhizomorpha takes precedence and should replace the nameArmillaria. To avoid this, a 2021 paper by Stalpers et al. proposes that the nameArmillaria should be protected. The proposal awaits decisions by theNomenclature Committee for Fungi and eventually by anInternational Botanical Congress.[13][14][15]
The basidiocarp (reproductive structure) of the fungus is amushroom that grows on wood, typically in small dense clumps or tufts. Theircaps (mushroom tops) are typically yellow-brown, somewhat sticky to touch when moist, and, depending on age, may range in shape fromconical toconvex to depressed in the center. Thestipe (stalk) may or may not have aring. AllArmillaria species have a whitespore print and none have avolva (cup at base).[16]
Armillaria species are long-lived and form thelargest living fungi in the world.[17] The largest known organism (of the speciesA. ostoyae) covers more than 3.4 square miles (8.8 km2) inOregon'sMalheur National Forest and is estimated to be 2,500 years old.[18][19] Some species displaybioluminescence, known asfoxfire.
Similar species includePholiota spp. which also grow in cespitose (mat-like) clusters on wood and fruit in the fall.Pholiota spp. are separated from Armillaria by its yellowish to greenish-yellow tone and a dark brown to grey-brown spore print.Mushroom hunters need to be wary ofGalerina spp. which can grow side by side withArmillaria spp. on wood.Galerina have a dark brown spore print and are deadlypoisonous (alpha-amanitin).
The white spore print and lack of volva can be compared toAmanita.[16] As awhite rot, it is distinguished fromTricholoma, amycorrhizal (non-parasitic) genus.
Honey fungus is a white-rot fungus, which is apathogenic organism that affects trees,shrubs, woody climbers and rarely, woody herbaceousperennial plants. Honey fungus can grow on living, decaying, and also dead plant material (being afacultative saprophyte). This means it can kill its host with little consequence, unlikeparasites that must moderate their growth to avoid host death.[19]
Honey fungus spreads from living trees, dead and live roots and stumps by means of reddish-brown to blackrhizomorphs (root-like structures) at the rate of approximately 3.3 feet (1 m) a year, but infection by root contact is possible. Infection by spores is rare. Rhizomorphs grow close to thesoil surface (in the top 7.9 inches (20 cm)) and invade new roots, or the root collar (where the roots meet the stem) of plants. An infected tree will die once the fungus hasgirdled it, or when significant root damage has occurred. Additionally, Infections can occur through the activity of wood boring beetles. For example,Agrilus biguttatus most commonly girdle inoak trees, which allows fungi to grow in the stems of these infected trees. This can happen rapidly, or may take several years. Infected plants will deteriorate, although may exhibit prolific flower or fruit production shortly before death.[why?]
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Initial symptoms of honey fungus infection includedieback or shortage of leaves in spring. Rhizomorphs (also called mycelial cords) appear under thebark and around the tree, and mushrooms grow in clusters from the infected plant in autumn and die back after the first frost. However thesesymptoms and signs do not necessarily mean that the pathogenic strains of honey fungus are the cause, so other identification methods are advised before diagnosis. Thin sheets of cream colored mycelium, beneath the bark at the base of the trunk or stem indicated that honey fungus is likely the pathogen. It will give off a strong mushroom scent and the mushrooms sometimes extend upward. Onconifers honey fungus often exudes a gum orresin from cracks in the bark.
Potentialhosts includeconifers and variousmonocotyledonous anddicotyledonous trees,shrubs, and herbaceous species, ranging from asparagus and strawberry to large forest trees (Patton and Vasquez Bravo 1967).[20]Armillaria root rot enters hosts through the roots. In Alberta, 75% of trap logs (Mallett and Hiratsuka 1985)[21] inserted into the soil between planted spruce became infected with the distinctive white mycelium ofArmillaria within one year. Of the infestations, 12% wereA. ostoyae, and 88% wereA. sinapina (Blenis et al. 1995).[22] Reviews of the biology, diversity, pathology, and control ofArmillaria in Fox (2000)[23] are useful.
Honey fungus are regarded in Ukraine, Russia, Poland, Germany and other European countries as one of the best wild mushrooms. They are commonly ranked abovemorels andchanterelles and only thecep/porcini is more highly prized.[citation needed] However, honey fungus must be thoroughly cooked as they are mildly poisonous raw. Honey mushrooms are one of four UK species that can cause sickness when ingested with alcohol. For those unfamiliar with the species, it is advisable not to drink alcohol for 12 hours before and 24 hours after eating this mushroom to avoid any possible nausea and vomiting. However, if these rules are followed, this variety of mushroom is a delicacy with a distinctive mushroomy and nutty flavour.[citation needed] Reference texts for identification areCollins Complete British Mushrooms and Toadstools for the variety of field pictures in it, and Roger Philips'Mushrooms for the quality of his out of field pictures and descriptions.
In Norway, some mycologists have started to regard honey fungus as poisonous, as the Norwegian health ministry is moving away from theparboiling practice.[24][25]
