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

trees. The brackets burst out from the bark of the tree, and these fruit bodies 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'' 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'' than to ''Piptoporus'', and the fungus was reclassified to ''Fomitopsis'' in 2016. The

specific epithet In taxonomy, binomial nomenclature ("two-term naming system"), also called nomenclature ("two-name naming system") or binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, bo ...

''betulina'' refers to the genus of the host plant ('' Betula'').

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 contrast ...

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 or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, ...

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

mycelium Mycelium (plural mycelia) is a root-like structure of a fungus consisting of a mass of branching, thread-like hyphae. Fungal colonies composed of mycelium are found in and on soil and many other substrates. A typical single spore germinates ...

, often smell distinctly of green apples. The

s are cylindrical to

ellipsoid An ellipsoid is a surface that may be obtained from a sphere by deforming it by means of directional scalings, or more generally, of an affine transformation. An ellipsoid is a quadric surface; that is, a surface that may be defined as th ...

al in shape, and measure 3–6 by 1.5–2

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

. ''Fomitopsis betulina'' has a bipolar mating system where monokaryons or germinating spores can only mate and form a fertile dikaryon 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 (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution. ::"The chrom ...

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, Bas ...

species, which involves two genes. It is considered inedible.

Range 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 as being in the same celestial hemisphere relative to the invariable plane of the solar system as Earth's Nort ...

, including

Northern America Northern America is the northernmost subregion of North America. The boundaries may be drawn slightly differently. In one definition, it lies directly north of Middle America (including the Caribbean and Central America).Gonzalez, Joseph. 20 ...

, Europe, and Asia. It is only found on

trees, including '' Betula pendula'', '' 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 close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson h ...

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 is present, lines of intraspecific antagonism 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 Sy ...

s of the fungus moth ''

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 in we ...

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

Research on chemical constituents

''Fomitopsis betulina'' has been widely used in

traditional medicine Traditional medicine (also known as indigenous medicine or folk medicine) comprises medical aspects of traditional knowledge that developed over generations within the folk beliefs of various societies, including indigenous peoples, before the ...

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 an ...

and pharmacological activity.

Phytochemicals Phytochemicals are chemical compounds produced by plants, generally to help them resist fungi, bacteria and plant virus infections, and also consumption by insects and other animals. The name comes . Some phytochemicals have been used as pois ...

include

phenolic acid Phenolic acids or phenolcarboxylic acids are 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 naturally occurring types of ph ...

indole Indole is an aromatic heterocyclic organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other c ...

compounds,

sterol Sterol is an organic compound with formula , whose molecule is derived from that of gonane by replacement of a hydrogen atom in position 3 by a hydroxyl group. It is therefore an alcohol of gonane. More generally, any compounds that contain the go ...

s, and

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

Agaric acid Agaric acid, also known as agaricin or 2-hydroxynonadecane-1,2,3-tricarboxylic acid, is an organic tricarboxylic acid (fatty acid) found in fungi, e.g. ''Laricifomes officinalis''. Its molecular formula is C22H40O7. Chemical properties Agari ...

found in the fruit body of the fungus, is poisonous to the parasitic whipworm ''Trichuris trichura''. The fungus was carried by " Ötzi the Iceman" – the 5,300 year old

mummy A mummy is a dead human or an animal whose soft tissues and organs have been preserved by either intentional or accidental exposure to chemicals, extreme cold, very low humidity, or lack of air, so that the recovered body does not decay fu ...

found in

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

, 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 polish the blade of a straight razor, a knife, or a wood ...

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

tinder Tinder is easily combustible material used to 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 until it bursts into flame. The flaming tinder i ...

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 two ...

References