text: lactarius torminosus lactarius torminosus , commonly known as the woolly milkcap or the bearded milkcap , is a large agaric fungus . a common and widely distributed species , it is found in north africa , northern asia , europe , and north america . it was first described scientifically by jacob christian schäffer in 1774 as an agaricus , and later transferred to the genus lactarius in 1821 by samuel frederick gray . a variety , l. torminosus var. nordmanensis , is known from the united states , canada , and switzerland . l. torminosus officially became the type species of lactarius in 2011 after molecular studies prompted the taxonomic reshuffling of species between several russulaceae genera . a mycorrhizal species , l. torminosus associates with various trees , most commonly birch , and its fruit bodies ( mushrooms ) grow on the ground singly or in groups in mixed forests . the caps of l. torminosus mushrooms are convex with a central depression , and attain a diameter of up to 10 cm ( 3 . 9 in ) . a blend of pink and ochre hues , the cap sometimes has concentric zones of alternating lighter and darker shades . the edge of the cap is rolled inward , and shaggy when young . on the underside of the cap are narrow flesh - colored gills that are crowded closely together . the cylindrical stem is a pale flesh color with a delicately downy surface and brittle flesh ; it is up to 8 cm ( 3 . 1 in ) long and 0 . 6 – 2 cm ( 0 . 2 – 0 . 8 in ) thick . when cut or injured , the fruit bodies ooze a bitter white latex that does not change color upon exposure to air . the variety nordmanensis , in contrast , has latex that changes from white to yellow . lactarius torminosus can be distinguished from similar species like l. pubescens or l. villosus by differences in morphology and coloration , or by microscopic characteristics like spore shape and size . although it is valued for its peppery flavor and eaten after suitable preparation in russia and finland , the species is highly irritating to the digestive system when eaten raw . the toxins , also responsible for the strongly bitter or acrid taste , are destroyed by cooking . studies have identified several chemicals present in the mushrooms , including ergosterol and derivatives thereof , and the pungent - tasting . taxonomy and phylogeny german naturalist jacob christian schäffer was the first to describe the species , placing it in agaricus in 1774 . seven years later in 1781 , jean bulliard described a species he called agaricus necator and illustrated it in the first volume of his herbier de la france ; this name and the synonym lactarius necator , resulting from christian hendrik persoon 's 1800 transfer to lactarius , are both considered to refer to l. torminosus . otto kuntze , for his part chose to put it in lactifluus , while paul kummer thought galorrheus was the appropriate placement ; until the recent resurrection of lactifluus , both genera had been long considered to be unnecessary segregates of lactarius . according to index fungorum , another synonym is samuel frederick gray 's lactarius . gray also gave the species its modern name when he transferred it to lactarius in his 1821 natural arrangement of british plants . the specific epithet torminosus means " tormenting " or " causing colic " , in reference to the gastrointestinal distress associated with consuming the raw mushroom . early english vernacular names were gray 's " milk - stool " ( 1821 ) , and james edward smith 's " bearded pepper agaric " ( 1824 ) . more recent common names include " shaggy milkcap " , " milkcap " , " pink - fringed milkcap " , " bearded milkcap " , and the british mycological society - recommended " woolly milkcap " . according to hesler and smith 's 1979 classification of the genus lactarius , l. torminosus belongs to subgenus piperites , section piperites ( in which it is the type species ) , subsection piperites . species in this subsection are characterized by having latex that does not turn yellow after exposure to air , and / or that does not stain the cut surface of the mushroom surface yellow . a 2004 phylogenetic analysis of european lactarius species concluded that l. torminosus falls into a group that includes l. , and that these two species are closely related to a group that includes l. , l. scoticus , and l. pubescens . a multi - gene molecular analysis published in 2008 demonstrated that species then distributed in the genera lactarius and russula actually consisted of four distinct lineages . the subsequent reorganization of russulaceae species — a taxonomic change needed to make russula and lactarius monophyletic — required that a new type species be defined for lactarius , since the previous type , l. piperatus , belonged to the clade that will be transferred to genus lactifluus . a proposal to conserve lactarius with l. torminosus as the type was accepted by the committee for fungi and passed at the 2011 international botanical congress . the change minimizes " taxonomic disruption " , allowing most of the common and well - known lactarius species to retain their names . description the cap is initially convex , but as it matures the center forms a depression and the outer edges rise until it assumes the shape of a shallow funnel ; its final width is typically between 2 and 12 cm ( 0 . 8 and 4 . 7 in ) . the cap margin is strongly curled inward ; when young , it is tomentose ( covered with a thick matting of hairs ) , forming a veil - like structure that partly covers up the gills . this tomentum diminishes with age . the cap surface is at first similarly tomentose , but eventually the hairs wear off , leaving the surface more or less smooth . the surface starts off somewhat sticky with clear concentric rings of darker shade ( a zonate pattern ) ; these rings , especially the outer ones , usually fade in maturity . the cap color is pinkish - orange to pale dull pink , becoming orange to whitish toward the margin as the pink gradually fades . the white to flesh - colored flesh is firm and brittle , but becomes flaccid in age . the latex that is produced when the mushroom tissue is cut or injured is white to cream , and does not change color with prolonged exposure to air , nor does it stain the gills . it has an acrid taste , with a slight to pungent odor . the gills are subdecurrent ( running only a small way down the length of the stem ) , close to crowded together , narrow , and sometimes forked near the stem . their color is whitish , becoming pink - tinged , turning pale tan with age . the adult stem is 1 . 5 – 8 cm ( 0 . 6 – 3 . 1 in ) long , 0 . 6 – 2 cm ( 0 . 2 – 0 . 8 in ) thick , fragile , more or less equal in width throughout , and cylindrical or narrowed at the base . its surface is dry , and either smooth to pruinose ( covered with a very fine whitish powder on the surface ) . the color ranges from pale light pink to yellowish - tinged or slightly pinkish orange to orange white , sometimes spotted . the interior of the stem is firm , beige white , and filled with a soft pith , but it eventually becomes hollow . occasionally , white mycelium is visible at the base of the stem where it meets the ground . the fruit body formation of l. torminosus is . in this type of development , the hymenium forms early on the underside of the cap and upper stem of the mushroom primordium . as the cap enlarges , the margin , made of flaring filamentous hyphae that grow outward and downward , tends to curve inward , eventually forming a flap of tissue roughly parallel to the stem surface . as further development takes place , these hyphae make contact with and adhere to the hymenial surface of the stem , covering basidia and ( very long cystidia ) already present . the junction between the two tissues produces a cavity that provides some temporary protection to the basidia , although they are already fertile when the cap margin starts to grow . microscopic characteristics the spore print of l. torminosus is cream to pale yellow , and the spores 8 – 10 . 2 by 5 . 8 – 6 . 6 μm , roughly spherical to broadly elliptical in side view , and hyaline ( translucent ) . only the ornamentation on their surface is amyloid ; it is partially reticulate ( network - like ) with interrupted ridges roughly 0 . 5 – 0 . 7 μm high , and a few isolated warts . spores have a conspicuous apiculus , demarcating where it was once attached to the basidia via the sterigma . the basidia are four - spored , hyaline and club - shaped to cylindrical , measuring 30 – 47 . 7 by 7 . 3 – 8 . 2 μm . pleurocystidia are only present in the form of embedded and originating in the hymenium and just below it , they reach 40 . 3 – 80 . 0 by 5 . 1 – 9 . 5 μm . are abundant in the hymenium . characterized by their spindle - shaped to ventricose ( swollen on one side ) form that gradually tapers in width , they have granular hyaline contents . gill edge cystidia ( cheilocystidia ) are smaller : 30 – 52 by 4 . 5 – 8 . 0 μm . the cap cuticle is made of gelatinized , interwoven hyphae arranged more or less parallel to the cap surface ( a form known as ixocutis ) ; the thin - walled , threadlike hyphae of this layer are 2 . 5 – 7 . 3 μm wide . variety nordmanensis lactarius nordmanensis was described by alexander smith in 1960 to account for a north american species closely resembling l. torminosus in appearance , but with a slightly larger range of spore sizes ( 9 – 11 by 6 . 5 – 8 μm ) . in contrast to the unchanging latex of l. torminosus , l. nordmanensis has whitish latex that slowly changes to pale yellow upon exposure to air ; the latex also stains mushroom tissues and paper yellow . hesler and smith reduced l. nordmanensis to the status of a variety under l. torminosus in 1979 . lactarius torminosus var. nordmanensis has been recorded from california , idaho , michigan , and wisconsin in the united states , quebec in canada , and switzerland . the variety resembles lactarius pubescens var. , but differs in its longer pleurocystidia , larger spores with slightly different spore ornamentation , and strongly burning acrid taste . the holotype specimen of l. torminosus var. nordmanensis was collected by smith in 1956 near nordman , idaho . similar species the woolly cap margin , pinkish tones in the cap , acrid latex , and association with birch are reliable field characteristics to help identify l. torminosus . however , there are several hairy lactarius species with which it is often confused , and sometimes examination of microscopic characteristics is necessary to distinguish between them . the closely related l. torminosus is a dwarf version of l. torminosus , an arctic species associated with the birches betula nana or b. glandulosa . immature fruit bodies of l. scrobiculatus resemble l. torminosus , but they have a white latex that soon turns yellow upon exposure to air , and their stems have shiny depressed spots . the caps of the poorly known species l. are not zonate , and its spores are smaller . l. pubescens is physically quite similar , but can be distinguished by its paler color and smaller spores ( 6 . 0 – 7 . 5 by 5 . 0 – 6 . 5 μm ) . l. has a cap margin that is not as hairy , whitish to cream - colored gills , and larger spores measuring 7 . 5 – 10 by 6 – 7 . 5 μm . l. has a coloration similar to l. torminosus , but is rarer and typically found associated with oak trees on calcareous soil . known only from north carolina and western canada , l. was named for its similarity to l. torminosus . it can be distinguished by its mild - tasting latex and smaller , roughly spherical spores measuring 5 . 5 – 7 by 5 . 5 – 6 . 5 μm . edibility and toxicity the intensely peppery taste of the raw mushroom can blister the tongue if sampled in excess . some authors have reported the species as outright poisonous , or causing " mild to fatal gastroenteritis " . in a 1930 publication , hans reported that although the mushroom was not toxic to " unicellular and cold - blooded organisms " when ingested , the liquid extract and the pressed juice of the fruit bodies , when injected under the skin of a frog , resulted in disturbed breathing , paralysis , and eventually death . symptoms that are typically experienced after consuming raw mushrooms include nausea , vomiting , and severe diarrhea that starts about one hour after ingestion . this combination can lead to dehydration , muscle spasms , and circulatory collapse . the gastroenteritis will usually resolve without treatment in a couple of days . despite these reports of toxicity , l. torminosus mushrooms are prepared in finland , russia , and other northern and eastern european countries by parboiling , soaking in brine for several days , or pickling , after which it is valued for its peppery taste . in norway , it is roasted and added to coffee . mushrooms are harvested for commercial sale in finland . the nutrient composition of finnish specimens has been analyzed and found to contain the following components ( as a percentage of dry weight ) : protein , 17 . 2 % ; phosphorus , 0 . 46 % ; calcium , 0 . 12 % ; magnesium , 0 . 088 % ; potassium , 2 . 97 % ; sodium 0 . 011 % . chemistry the compound thought to be responsible for the toxicity of raw l. torminosus is the pungent - tasting present at a concentration of 0 . 16 mg / g mushroom . is a breakdown product of - . broken lactifers — specialized hyphal cells that produce the mushroom 's latex — leak the precursor chemicals whose breakdown products act as the defensive agents toxic to humans , effectively deterring certain vertebrates that might consume the mushroom . the lactarane - type sesquiterpene lactone 15 - a is one of several sesquiterpenes produced by the species . other are found in various lactarius species , such as blennin a in l. deliciosus and l. blennius , and lactarorufin n in lactarius rufus . fungal sesquiterpenes are commonly produced as toxins to defend against predation , and as a result some have chemical properties that may have applications in medicinal chemistry . fruit bodies of lactarius torminosus contain a number of sterols , of which ergosterol ( a component of fungal cell walls ) is the most predominant at 60 . 5 % of all sterols , followed by its derivatives and ergosta - 5 / 7 - dien - 3 - ol ( 17 . 0 % ) , - 7 - en - 3 - ol ( 13 . 7 % ) and ergosta - 7 - 22 - dien - 3 - ol ( 8 . 3 % ) . researchers have identified 28 volatile compounds that contribute to the odor of the mushroom . many of these are alcohols and carbonyl compounds with eight carbon atoms ; the predominant volatile compound ( about 90 % ) is 1 - octen - 3 - one , an common in mushrooms . ecology and distribution lactarius torminosus is a mycorrhizal species , and as such plays an important role in facilitating nutrient and water uptake by trees . it grows in association with birch ( betula ) and hemlock ( tsuga ) in mixed forests . it is also known to grow in urban settings when birch trees are nearby . a field study in scotland concluded that the species is more likely to be present in older than in younger birch woodlands . fruit bodies grow on the ground , scattered or grouped together . they are a component of the diet of the red squirrel , and serve as breeding sites for some fungus - feeding flies in the drosophilidae and mycetophilidae families . lactarius torminosus mushrooms may be parasitized by the mold hypomyces , which produces a cream - ochre to cinnamon - colored granular or velvety growth of mycelium on the surfaces of the gills and causes them to be deformed . the species is found in northern temperate and boreal climates , penetrating sometimes into subarctic regions . it has been recorded from north africa , northern asia , europe , and is common in north america , where it sometimes grows with aspen ( populus species ) . the north american distribution extends north into the yukon and alaska and south to mexico .