page:  = Mycena <unk> = 
   
   Mycena <unk> , commonly known as the clustered bonnet or the oak @-@ stump bonnet cap , is a species of mushroom in the family <unk> . The <unk> edible mushroom has a reddish @-@ brown bell @-@ shaped cap up to 4 @.@ 5 cm ( 1 @.@ 8 in ) in diameter . The thin stem is up to 9 cm ( 3 @.@ 5 in ) tall , whitish to yellow @-@ brown at the top but progressively becoming reddish @-@ brown towards the base in maturity , where they are covered by a yellowish mycelium that can be up to a third of the length of the stem . The gills are pale brown to pinkish , and the spore print is white . It is a widespread saprobic fungus , and has been found in Europe , North Africa , Asia , <unk> , and North America , where it grows in small groups or <unk> on fallen logs and stumps , especially of oak . British mycologist <unk> Corner has described two varieties of the mushroom from Borneo . <unk> species with which M. <unk> may be confused include M. galericulata and M. <unk> . 
   
   = = Taxonomy , phylogeny , and naming = = 
   
   First described as Agaricus <unk> by Swedish mycologist Elias Magnus Fries in 1838 , it was assigned its current name in 1872 by <unk> <unk> . Mycena galericulata var. <unk> ( named by <unk> in 1879 ) , and its <unk> Agaricus <unk> var. <unk> ( named by Fries in 1873 ) , are synonyms . 
   In a molecular study of the large <unk> ribosomal DNA sequences of mycorrhizal fungi of the <unk> <unk> <unk> , M. <unk> was found to be closely related to M. <unk> , M. <unk> , and M. <unk> . 
   The specific epithet <unk> means " bent in " . The mushroom is commonly known as the " clustered bonnet " or the " oak @-@ stump bonnet cap " . 
   
   = = Description = = 
   
   The cap is light reddish @-@ brown , with a diameter typically ranging from 1 to 4 @.@ 5 cm ( 0 @.@ 4 to 1 @.@ 8 in ) . Initially <unk> to bell @-@ shaped to convex , it <unk> during maturity , developing visible surface grooves corresponding to the gills underneath the cap . The margin of the cap has minute but distinct <unk> . The surface is moist and smooth , and <unk> . The cap frequently develops splits in the margin , or cracks in the disc ( the central part of the cap ) . The flesh of the cap is thick in the center but thin elsewhere , grayish to whitish , fragile , and with a slightly <unk> odor and taste . The gills have a <unk> attachment to the stem ( that is , running down the length of the stem ) and are a pale brownish color with <unk> of red . They are broad ( between 3 and 6 mm ) , and have a close to <unk> spacing , with about 26 – 35 gills reaching the stem . The fragile stem is 3 to 9 cm ( 1 @.@ 2 to 3 @.@ 5 in ) long by 0 @.@ 15 to 0 @.@ 4 cm ( 0 @.@ 06 to 0 @.@ 16 in ) thick and yellow to yellow @-@ brown , becoming reddish @-@ brown to orange @-@ brown in the bottom half in maturity . The lower portion of young stems is covered with white <unk> . Roughly equal in thickness at the top and bottom , the base of the stem is covered by a yellowish mycelium that can be up to a third of the length of the stem . The edibility of the mushroom is " doubtful " and consumption " best avoided " . 
   
   = = = Microscopic characteristics = = = 
   
   The spores are 7 – 9 by 5 – 6 @.@ 5 μm , broadly ellipsoid , smooth , and strongly amyloid ( it turns black when treated with Melzer 's reagent ) . The basidia ( spore @-@ bearing cells ) are four @-@ spored . The <unk> ( cystidia on the gill face ) are not differentiated . The cheilocystidia ( cystidia on the gill edge ) are embedded in the gill edge and very inconspicuous , club @-@ shaped , 26 – 36 by 5 – 10 μm , and have tips that are covered with <unk> projections that can be slender or thick . The flesh of the gills is <unk> , and pale yellowish to dirty brown when stained in iodine . The flesh of the cap has a distinct <unk> , a well @-@ differentiated <unk> ( a region of tissue immediately under the <unk> ) , and a <unk> <unk> body ( gill tissue ) ; it is pale yellowish to <unk> brownish in iodine stain . 
   
   = = = <unk> = = = 
   
   <unk> Corner defined the varieties M. <unk> var. <unk> and var. <unk> in his 1994 publication on <unk> mushrooms of <unk> , a <unk> region <unk> the boundary of the <unk> and <unk> <unk> . The variety <unk> ( named after its type locality , <unk> ) has a cap margin that is not <unk> , little or no odor , and cheilocystidia with shorter processes . It was found growing on the dead wood of <unk> <unk> , a stone oak tree in the beech family . Variety <unk> , found in <unk> , has spores that are almost spherical . 
   
   = = = Similar species = = = 
   
   Mycena <unk> bears some resemblance to M. <unk> , but is only associated with decaying hardwood logs and stumps , and is found in eastern North America , and sometimes on oak on the West Coast . In age , it develops reddish spots on the gills that are not seen in M. <unk> . M. <unk> is often confused with the edible M. galericulata , a common species that is variable in cap color , size and shape . M. galericulata typically has a <unk> conical cap that is dull gray @-@ brown , and white to grayish veins that have numerous cross @-@ veins . M. <unk> has a <unk> stem that is bluish @-@ gray . 
   
   = = Habitat and distribution = = 
   
   Mycena <unk> is a saprobic fungus , deriving its nutrients from decomposing organic matter found in plant litter such as leaves , twigs , bark and branches . It <unk> this by producing enzymes capable of breaking down the three major biochemical components of plant cell walls found in litter : <unk> , <unk> and lignin . 
   The fruit bodies of Mycena <unk> grow in dense groups or clusters on decaying hardwood logs and stumps ( especially oak and chestnut ) during the spring and autumn . The fungus forms a white , <unk> mycelium on the surface of decomposing oak leaves . Occasionally , it can be found growing on a living tree . In eastern North America , it is abundant in the area bounded by Nova Scotia , Ontario , Manitoba , Missouri , North Carolina , and New York . It has been found in Oregon , but the species appears to be generally rare along the Pacific Coast . The range of the fungus also includes Europe , the Canary Islands , North Africa , East Siberia , Japan , <unk> , Turkey , and New Zealand . 
   
   = = Chemistry = = 
   
   In a study of the trace metal concentrations of various mushrooms species found in <unk> ( Turkey ) , M. <unk> was found to have comparatively high levels of iron ( 628 mg per kg ) and nickel ( 21 @.@ 6 mg / kg ) , measured on a dry weight basis . Laboratory studies have shown that the fungus is resistant to aluminum . The fungus has been investigated for its ability to <unk> synthetic <unk> that are used in the textile , <unk> , <unk> and <unk> industries . The <unk> are not readily biodegradable , and when discharged into the environment are persistent and many are toxic . 
   
   