''Fomitopsis betulina'' (previously ''Piptoporus betulinus''), commonly known as the birch polypore, birch bracket, or razor strop, is a common

bracket fungus A bracket is either of two tall fore- or back-facing punctuation marks commonly used to isolate a segment of text or data from its surroundings. They come in four main pairs of shapes, as given in the box to the right, which also gives their n ...

and, as the name suggests, grows almost exclusively on

birch A birch is a thin-leaved deciduous hardwood tree of the genus ''Betula'' (), in the family Betulaceae, which also includes alders, hazels, and hornbeams. It is closely related to the beech- oak family Fagaceae. The genus ''Betula'' contains 3 ...

trees. The brackets burst out from the bark of the tree, and these

fruit bodies The sporocarp (also known as fruiting body, fruit body or fruitbody) of fungi is a multicellular structure on which spore-producing structures, such as basidia or asci, are borne. The fruitbody is part of the sexual phase of a fungal life cyc ...

can last for more than a year.

Taxonomy

The fungus was originally described by Jean Bulliard in 1788 as ''Boletus betulinus''. It was transferred to the genus ''

Piptoporus ''Piptoporus'' is a genus of bracket fungi in the family Fomitopsidaceae. Species Various species formerly classified as ''Piptoporus'' (for example, ''P. choseniae'', ''P. fraxineus'', ''P. ulmi'', ''P. hirtus'', and ''P. elatinus'') have been ...

'' by

Petter Karsten Petter Adolf Karsten (16 February 1834 – 22 March 1917) was a Finnish mycologist, the foremost expert on the fungi of Finland in his day, and known in consequence as the "father of Finnish mycology". Karsten was born in Merimasku near Turku ...

in 1881.

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 ...

studies suggested that the species was more closely related to ''

Fomitopsis ''Fomitopsis'' is a genus of more than 40 species of bracket fungi in the family Fomitopsidaceae. Taxonomy The genus was circumscribed by Finnish mycologist Petter Karsten in 1881 with '' Fomitopsis pinicola'' as the type species. Molecular an ...

'' than to ''Piptoporus'', and the fungus was reclassified to ''Fomitopsis'' in 2016. The

specific epithet In Taxonomy (biology), taxonomy, binomial nomenclature ("two-term naming system"), also called binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin gramm ...

''betulina'' refers to the genus of the

host A host is a person responsible for guests at an event or for providing hospitality during it. Host may also refer to: Places * Host, Pennsylvania, a village in Berks County * Host Island, in the Wilhelm Archipelago, Antarctica People * ...

plant (''

Betula A birch is a thin-leaved deciduous hardwood tree of the genus ''Betula'' (), in the family Betulaceae, which also includes alders, hazels, and hornbeams. It is closely related to the beech- oak family Fagaceae. The genus ''Betula'' contains 3 ...

'').

Common name In biology, a common name of a taxon or organism (also known as a vernacular name, English name, colloquial name, country name, popular name, or farmer's name) is a name that is based on the normal language of everyday life; and is often con ...

s for the fungus include birch bracket, birch polypore, and razorstrop fungus.

Description

The fruit bodies (

basidiocarp In fungi, a basidiocarp, basidiome, or basidioma () is the sporocarp of a basidiomycete, the multicellular structure on which the spore-producing hymenium is borne. Basidiocarps are characteristic of the hymenomycetes; rusts and smuts do no ...

s) are pale, with a smooth greyish-brown top surface, while the creamy white underside has hundreds of pores that contain the

spore In biology, a spore is a unit of sexual reproduction, sexual (in fungi) or asexual reproduction that may be adapted for biological dispersal, dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores fo ...

s. The fruit body has a rubbery texture, becoming corky with age. Wood decayed by the fungus, and cultures of its

mycelium Mycelium (: mycelia) is a root-like structure of a fungus consisting of a mass of branching, thread-like hyphae. Its normal form is that of branched, slender, entangled, anastomosing, hyaline threads. Fungal colonies composed of mycelium are fo ...

, often smell distinctly of green apples. The

s are cylindrical to

ellipsoid An ellipsoid is a surface that can be obtained from a sphere by deforming it by means of directional Scaling (geometry), scalings, or more generally, of an affine transformation. An ellipsoid is a quadric surface; that is, a Surface (mathemat ...

al in shape, and measure 3–6 by 1.5–2

μm The micrometre (Commonwealth English as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American English), also commonly known by the non-SI term micron, is a unit of length in the International System ...

. ''Fomitopsis betulina'' has a bipolar mating system where

monokaryon A monokaryon is a fungal mycelium or hypha in which each cell contains a single nucleus. It also refers to a mononuclear spore or cell of a fungus that produces a dikaryon in its life cycle.dikaryon The dikaryon (karyogamy) is a cell nucleus feature that is unique to certain fungi. (The green alga '' Derbesia'' had been long considered an exception, until the heterokaryotic hypothesis was challenged by later studies.) Compatible cell-types c ...

with an individual that possesses a different mating-type factor. There are at least 33 different mating-type factors within the British population of this fungus. These factors are all variants or

allele An allele is a variant of the sequence of nucleotides at a particular location, or Locus (genetics), locus, on a DNA molecule. Alleles can differ at a single position through Single-nucleotide polymorphism, single nucleotide polymorphisms (SNP), ...

s of a single gene, as opposed to the tetrapolar mating system of some other

basidiomycete Basidiomycota () is one of two large divisions that, together with the Ascomycota, constitute the subkingdom Dikarya (often referred to as the "higher fungi") within the kingdom Fungi. Members are known as basidiomycetes. More specifically, Basid ...

species, which involves two genes.

Distribution, habitat and ecology

''Fomitopsis betulina'' is one of the most common species of brown rot fungi. The geographic distribution of ''F. betulina'' appears to be restricted to the

Northern Hemisphere The Northern Hemisphere is the half of Earth that is north of the equator. For other planets in the Solar System, north is defined by humans as being in the same celestial sphere, celestial hemisphere relative to the invariable plane of the Solar ...

, including Northern America, Europe, and Asia. It is only found on

trees, including ''

Betula pendula ''Betula pendula'', commonly known as silver birch, warty birch, European white birch, or East Asian white birch, is a species of tree in the family (biology), family Betulaceae, native plant, native to Europe and parts of Asia, though in so ...

'', '' B. pubescens'', '' B. papyrifera'', and '' B. obscura''. There is some doubt about the ability of isolates from the European continent, North America and the British Isles to interbreed. It is a necrotrophic

parasite Parasitism is a Symbiosis, close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the Host (biology), host, causing it some harm, and is Adaptation, adapted str ...

on weakened birches, and will cause brown rot and eventually death, being one of the most common fungi visible on dead birches. It is likely that the birch bracket fungus becomes established in small wounds and broken branches and may lie dormant for years, compartmentalised into a small area by the tree's own defence mechanisms, until something occurs to weaken the tree. Fire, drought and suppression by other trees are common causes of such stress. In most infections there is only one fungal individual present, but occasionally several individuals may be isolated from a single tree, and in these cases it is possible that the birch bracket fungus entered after something else killed the tree. These fungal "individuals" can sometimes be seen if a slice of brown-rotted birch wood is incubated in a plastic bag for several days. This allows the white

of the fungus to grow out of the surface of the wood. If more than one individual

dikaryon The dikaryon (karyogamy) is a cell nucleus feature that is unique to certain fungi. (The green alga '' Derbesia'' had been long considered an exception, until the heterokaryotic hypothesis was challenged by later studies.) Compatible cell-types c ...

is present, lines of

intraspecific antagonism Intraspecific antagonism means a disharmonious or antagonistic interaction between two individuals of the same species. As such, it could be a sociology, sociological term, but was actually coined by Alan Rayner and Norman Kalmer Todd, Norman Todd ...

form as the two individual mycelia interact and repel each other. The fungus can harbor a large number of species of insects that depend on it for food and as breeding sites. In a large-scale study of over 2600 fruit bodies collected in eastern Canada, 257 species of arthropods, including 172 insects and 59 mites, were found. The fungus is eaten by the

caterpillar Caterpillars ( ) are the larval stage of members of the order Lepidoptera (the insect order comprising butterflies and moths). As with most common names, the application of the word is arbitrary, since the larvae of sawflies (suborder ...

s of the

fungus moth Tineidae is a family of moths in the order Lepidoptera described by Pierre André Latreille in 1810. Collectively, they are known as fungus moths or tineid moths. The family contains considerably more than 3,000 species in more than 300 genera. ...

Nemaxera betulinella __NOTOC__ ''Nemaxera'' is a genus of the fungus moth family, Tineidae. Therein, it belongs to the subfamily Nemapogoninae. The genus is considered monotypic, with the single species ''Nemaxera betulinella'' placed here. The species occurs i ...

''. Old fruit bodies that have survived the winter are often colonized by the white to pale yellow fungus ''

Hypocrea pulmonata ''Hypocrea'' is a genus of fungi in the family Hypocreaceae. The widespread genus is estimated to contain 171 species that grow on rotten wood, and are often associated with other fungi. Anamorphic genera associated with ''Hypocrea'' include '' ...

''.

Research on chemical constituents

''Fomitopsis betulina'' has been widely used in

traditional medicine Traditional medicine (also known as indigenous medicine or folk medicine) refers to the knowledge, skills, and practices rooted in the cultural beliefs of various societies, especially Indigenous groups, used for maintaining health and treatin ...

s, and has been extensively researched for its

phytochemistry Phytochemistry is the study of phytochemicals, which are chemicals derived from plants. Phytochemists strive to describe the structures of the large number of secondary metabolites found in plants, the functions of these compounds in human and ...

and

pharmacological Pharmacology is the science of drugs and medications, including a substance's origin, composition, pharmacokinetics, pharmacodynamics, therapeutic use, and toxicology. More specifically, it is the study of the interactions that occur between ...

activity.

Phytochemical Phytochemicals are naturally-occurring chemicals present in or extracted from plants. Some phytochemicals are nutrients for the plant, while others are metabolites produced to enhance plant survivability and reproduction. The fields of ext ...

s include

phenolic acid Phenolic acids or phenolcarboxylic acids ? are phenolic compounds and types of aromatic acid compounds. Included in that class are substances containing a phenolic ring and an organic carboxylic acid function (C6-C1 skeleton). Two important nat ...

indole Indole is an organic compound with the formula . Indole is classified as an aromatic heterocycle. It has a bicyclic structure, consisting of a six-membered benzene ring fused to a five-membered pyrrole ring. Indoles are derivatives of indole ...

compounds,

sterol A sterol is any organic compound with a Skeletal formula, skeleton closely related to Cholestanol, cholestan-3-ol. The simplest sterol is gonan-3-ol, which has a formula of , and is derived from that of gonane by replacement of a hydrogen atom on ...

s, and

triterpene Triterpenes are a class of terpenes composed of six isoprene units with the molecular formula C30H48; they may also be thought of as consisting of three terpene units. Animals, plants and fungi all produce triterpenes, including squalene, the pre ...

s, especially

betulin Betulin is an abundant, naturally occurring triterpene. It is commonly isolated from the bark of birch trees, hence its name, from '' betula''. It forms up to 30% of the dry weight of silver birch bark. It is also found in birch sap. '' Inono ...

and

betulinic acid Betulinic acid is a naturally occurring pentacyclic triterpenoid which has antiretroviral, antimalarial, and anti-inflammatory properties, as well as a more recently discovered potential as an anticancer agent, by inhibition of topoisomerase. ...

. Agaric acid, found in the fruit body of the fungus, is poisonous to the parasitic

whipworm ''Trichuris trichiura, Trichocephalus trichiuris'' or whipworm, is a parasitic roundworm (a type of helminth) that causes trichuriasis (a type of helminthiasis which is one of the neglected tropical diseases) when it infects a human large intest ...

''Trichuris trichiura''. The fungus was carried by "

Ötzi the Iceman Ötzi, also called The Iceman, is the natural mummy of a man who lived between 3350 and 3105 BC. Ötzi's remains were discovered on 19 September 1991, in the Ötztal Alps (hence the nickname "Ötzi", ) at the Austria–Italy border. He ...

" – the 5,300 year old

mummy A mummy is a dead human or an animal whose soft tissues and Organ (biology), organs have been preserved by either intentional or accidental exposure to Chemical substance, chemicals, extreme cold, very low humidity, or lack of air, so that the ...

found in

Tyrol Tyrol ( ; historically the Tyrole; ; ) is a historical region in the Alps of Northern Italy and western Austria. The area was historically the core of the County of Tyrol, part of the Holy Roman Empire, Austrian Empire and Austria-Hungary, f ...

, with speculation that the fungus may have been used as a

laxative Laxatives, purgatives, or aperients are substances that loosen stools and increase bowel movements. They are used to treat and prevent constipation. Laxatives vary as to how they work and the side effects they may have. Certain stimulant, lubri ...

to expel whipworm.

Uses

The velvety cut surface of the fruit body was traditionally used as a

strop A razor strop or simply a strop (sometimes called a razor strap or strap) is a flexible strip of leather, canvas, denim fabric, balsa wood, or other soft material, used to straighten and polishing, polish the blade of a straight razor, a knife, ...

for finishing the edges on razors, and as a mounting material for insect collections. It has also been used as

tinder Tinder is easily Combustibility and flammability, combustible material used to Firemaking, start a fire. Tinder is a finely divided, open material which will begin to glow under a shower of sparks. Air is gently wafted over the glowing tinder unt ...

and

anesthetic An anesthetic (American English) or anaesthetic (British English; see spelling differences) is a drug used to induce anesthesia ⁠— ⁠in other words, to result in a temporary loss of sensation or awareness. They may be divided into t ...

. It is considered inedible.

References