 = Astraeus hygrometricus = 
 
 Astraeus hygrometricus , commonly known as the hygroscopic earthstar , the barometer earthstar , or the false earthstar , is a species of fungus in the Diplocystaceae family . Young specimens resemble a puffball when young and <unk> . In maturity , the mushroom displays the characteristic earthstar shape that is a result of the outer layer of fruit body tissue splitting open in a star @-@ like manner . The false earthstar is an ectomycorrhizal species that grows in association with various trees , especially in sandy soils . A. hygrometricus has a cosmopolitan distribution , and is common in temperate and tropical regions . Its common names refer to the fact that it is hygroscopic ( water @-@ absorbing ) , and can open up its rays to expose the spore sac in response to increased humidity , and close them up again in drier conditions . The rays have an irregularly cracked surface , while the spore case is pale brown and smooth with an irregular slit or tear at the top . The gleba is white initially , but turns brown and powdery when the spores mature . The spores are reddish @-@ brown , roughly spherical with minute warts , measuring 7 @.@ 5 – 11 <unk> in diameter . 
 Despite a similar overall appearance , A. hygrometricus is not related to the true earthstars of genus Geastrum , although historically , they have been <unk> confused . The species was first described by <unk> <unk> Persoon in 1801 as Geastrum hygrometricus . In 1885 , Andrew P. Morgan proposed that differences in microscopic characteristics warranted the creation of a new genus Astraeus distinct from Geastrum ; this opinion was not universally accepted by later authorities . Several Asian populations formerly thought to be A. hygrometricus were renamed in the 2000s once phylogenetic analyses revealed they were unique Astraeus species , including A. asiaticus and A. odoratus . Research has revealed the presence of several <unk> chemical compounds in the fruit bodies . North American field guides typically rate A. hygrometricus as inedible . 
 
 = = Taxonomy , naming , and phylogeny = = 
 
 Because this species resembles the earthstar fungi of Geastrum , it was placed in that genus by early authors , starting with Christian <unk> Persoon in 1801 ( as <unk> , an alternate spelling of Geastrum ) . According to the American botanist Andrew P. Morgan , however , the species differed from those of Geastrum in not having open chambers in the young gleba , having larger and branched <unk> threads , not having a true hymenium , and having larger spores . Accordingly , Morgan set Persoon 's <unk> <unk> as the type species of his new genus Astraeus in 1889 . Despite Morgan 's publication , some authorities in the following decades continued to classify the species in Geastrum . The New @-@ Zealand based mycologist Gordon <unk> Cunningham explicitly transferred the species back to the genus Geastrum in 1944 , explaining : 
 The treatment of this species by certain <unk> well illustrates the pitfalls that lie in wait for those who worship at the shrine of <unk> classification ... The only feature of those outlined in which the species differs from others of Geastrum is the somewhat primitive hymenium . In the developing plant the <unk> cavities are separated by <unk> plates so tenuous as to be overlooked by the <unk> worker . Each cavity is filled with basidia somewhat irregularly arranged in clusters ( like those of Scleroderma ) and not in the definite palisade of the species which have been studied . This difference disappears as maturity is reached , when plants resemble closely the <unk> of any other member of the genus . The <unk> is then unable to indicate any point of difference by which " Astraeus " may be separated from Geastrum , which indicates that the name should be discarded . 
 Cunningham 's treatment was not followed by later authorities , who largely considered Astraeus a distinct genus . According to the <unk> authority <unk> , synonyms of Astraeus hygrometricus include <unk> <unk> <unk> . ( 1772 ) ; Geastrum <unk> <unk> . ( 1822 ) ; Geastrum <unk> ( <unk> . ) <unk> . ( 1885 ) ; and Astraeus <unk> <unk> ( 1900 ) . 
 Astraeus hygrometricus has been given a number of <unk> names that allude to its hygroscopic behavior , including the " <unk> earthstar " , the " hygroscopic earthstar " , the " barometer earthstar " , and the " water @-@ measure earthstar " . The resemblance to Geastrum species ( also known as true earthstars ) accounts for the common name " false earthstar " . The specific name is derived from the Greek words <unk> ( <unk> ) " wet " and <unk> ( <unk> ) " measure " . The German Mycological Society selected the species as their " Mushroom of the Year " in 2005 . 
 Studies in the 2000s showed that several species from Asian collection sites labelled under the specific epithet hygrometricus were actually considerably variable in a number of <unk> and microscopic characteristics . Molecular studies of the DNA sequences of the <unk> region of the ribosomal DNA from a number of Astraeus specimens from around the world have helped to clarify phylogenetic relationships within the genus . Based on these results , two Asian " hygrometricus " populations have been described as new species : A. asiaticus and A. odoratus ( synonymous with <unk> 's A. <unk> described in 2003 ) . Preliminary DNA analyses suggests that the European A. hygrometricus described by Persoon is a different species than the North American version described by Morgan , and that the European population may be divided into two distinct <unk> , from France and from the Mediterranean . A 2010 study identified a Japanese species , previously identified as A. hygrometricus , as genetically distinct ; it has yet to be officially named . 
 A form of the species found in Korea and Japan , A. hygrometricus var. koreanus , was named by <unk> <unk> in 1958 ; it was later ( 1976 ) published as a distinct species — A. koreanus — by <unk> <unk> . As pointed out by <unk> and colleagues , clarification of the proper name for this taxon must await analysis of A. hygrometricus var. koreanus specimens from the type locality in North Korea . 
 
 = = Description = = 
 
 Young specimens of A. hygrometricus have roughly spherical fruit bodies that typically start their development partially embedded in the substrate . A smooth whitish mycelial layer covers the fruit body , and may be partially encrusted with debris . As the fruit body matures , the mycelial layer tears away , and the outer tissue layer , the exoperidium , breaks open in a star @-@ shaped ( <unk> ) pattern to form 4 – 20 irregular " rays " . This simultaneously pushes the fruit body above ground to reveal a round spore case enclosed in a thin <unk> <unk> . The rays open and close in response to levels of moisture in the environment , opening up in high humidity , and closing when the air is dry . This is possible because the exoperidium is made of several different layers of tissue ; the innermost , fibrous layer is hygroscopic , and <unk> or <unk> the entire ray as it loses or gains moisture from its surroundings . This adaptation enables the fruit body to disperse spores at times of <unk> moisture , and reduce evaporation during dry periods . Further , dry fruit bodies with the rays curled up may be readily blown about by the wind , allowing them to scatter spores from the pore as they roll . 
 The fruit body is 1 – 8 cm ( 0 @.@ 4 – 3 @.@ 1 in ) in diameter from tip to tip when expanded . The exoperidium is thick , and the rays are typically <unk> ( divided into small areas by cracks and crevices ) on the upper surface , and are dark grey to black . The spore case is <unk> ( lacking a stalk ) , light gray to tan color and 1 to 3 cm ( 0 @.@ 4 to 1 @.@ 2 in ) broad with a felt @-@ like or <unk> ( coated with loose scaly crust ) surface ; the top of the spore case is opened by an irregular slit , tear or pore . The interior of the spore case , the gleba , is white and solid when young , and divided into oval <unk> — a characteristic that helps to distinguish it from Geastrum . The gleba becomes brown and powdery as the specimen matures . Small dark <unk> threads ( rhizomorphs ) extend from the base of the fruit body into the substrate . The rhizomorphs are fragile , and often break off after maturity . 
 The spores are spherical or nearly so , reddish @-@ brown , thick @-@ walled and <unk> ( covered with warts and spines ) . The spores ' dimensions are 7 – 11 µm ; the warts are about 1 µm long . The spores are non @-@ amyloid , and will not stain with iodine from Melzer 's reagent . The use of scanning electron microscopy has shown that the spines are 0 @.@ 90 – 1 @.@ 45 µm long , rounded at the tip , narrow , tapered , and sometime joined together at the top . The capillitia ( masses of thread @-@ like sterile fibers dispersed among the spores ) are branched , 3 @.@ 5 – 6 @.@ 5 µm in diameter , and hyaline ( translucent ) . The basidia ( spore @-@ bearing cells ) are <unk> to eight @-@ spored , with very short sterigmata . The basidia are arranged in long strings of clusters ; individual basidia measure 11 – 15 by 18 – 24 µm . The threads of the capillitia arise from the inner surface of the peridium , and are thick @-@ walled , long , interwoven , and branched , measuring 3 – 5 @.@ 5 µm thick . The exoperidium ( the outer layer of tissue , comprising the rays ) is made of four distinct layers of tissue : the mycelial layer contains branched hyphae that are 4 – 6 μm in diameter ; the hyphae of the fibrous layer are 6 – 8 μm diameter and branched ; the <unk> @-@ type layer has branched hyphae of 3 – 4 μm diameter ; the soft layer contains hyphae that are 3 – 6 μm in diameter . 
 
 = = = Edibility = = = 
 
 North American sources describe A. hygrometricus as being of either unknown edibility , or too tough to be edible . However , they are regularly consumed in Asia , including Nepal and South Bengal , where " local people consume them as delicious food " . They are collected from the wild and sold in the markets of India . 
 A study of a closely related southeast Asian Astraeus species concluded that the fungus contained an abundance of volatile eight @-@ carbon compounds ( including 1 @-@ <unk> , 1 @-@ <unk> @-@ 3 @-@ <unk> , and 1 @-@ <unk> @-@ 3 @-@ one ) that imparted a " mushroom @-@ like , <unk> , and pungent odor that was evident as an <unk> and moss @-@ like smell upon opening the caps " . The study 's authors further noted that the fruit bodies after cooking have a " roasted , <unk> , <unk> , and <unk> flavor " . <unk> compounds detected after cooking the mushroom samples included <unk> , <unk> , <unk> , and <unk> compounds . The regional differences in opinions on edibility are from sources published before it was known that North American and Asian versions of A. hygrometricus were not always the same ; in some cases Asian specimens have been identified as new species , such as A. asiaticus and A. odoratus . 
 
 = = Similar species = = 
 
 Although A. hygrometricus bears a superficial resemblance to member of the " true earthstars " Geastrum , it may be readily differentiated from most by the hygroscopic nature of its rays . <unk> earthstars include G. <unk> , G. <unk> , G. <unk> , G. <unk> , and G. <unk> . Unlike Geastrum , the young fruit bodies of A. hygrometricus do not have a <unk> ( sterile tissue in the gleba , at the base of the spore sac ) . Geastrum tends to have its spore sac opening surrounded by a <unk> or a disc , in contrast with the single <unk> slit of A. hygrometricus . There are also several microscopic differences : in A. hygrometricus , the basidia are not arranged in parallel columns , the spores are larger , and the threads of the capillitia are branched and continuous with the hyphae of the peridium . Despite these differences , older specimens can be difficult to distinguish from Geastrum in the field . One species of Geastrum , G. <unk> , does have thick and brittle rays that are moderately hygroscopic , and could be confused with A. hygrometricus ; however , its spores are smaller than A. hygrometricus , typically about 4 µm in diameter . 
 Astraeus <unk> is larger , 5 to 15 cm ( 2 @.@ 0 to 5 @.@ 9 in ) or more when expanded , and often has a more pronounced <unk> pattern on the inner surface of the rays . It is found in North America and the Canary Islands . A. asiaticus and A. odoratus are two similar species known from throughout Asia and Southeast Asia , respectively . A. odoratus is distinguished from A. hygrometricus by a smooth outer mycelial layer with few adhering soil particles , 3 – 9 broad rays , and a fresh odor similar to moist soil . The spore ornamentation of A. odoratus is also distinct from A. hygrometricus , with longer and narrower spines that often joined together . A. asiaticus has an outer <unk> surface covered with small granules , and a gleba that is purplish @-@ chestnut in color , compared to the smooth <unk> surface and brownish gleba of A. hygrometricus . The upper limit of the spore size of A. asiaticus is larger than that of its more common relative , ranging from 8 @.@ 75 – 15 @.@ 2 μm . A. koreanus ( sometimes named as the variety A. hygrometricus var. koreanus ; see Taxonomy ) differs from the more common form in its smaller size , paler fruit body , and greater number of rays ; microscopically , it has smaller spores ( between 6 @.@ 8 and 9 μm in diameter ) , and the spines on the spores differ in length and morphology . It is known from Korea and Japan . 
 
 = = Habitat , distribution , and ecology = = 
 
 Astraeus hygrometricus is an ectomycorrhizal fungus and grows in association with a broad range of tree species . The mutualistic association between tree roots and the mycelium of the fungus helps the trees extract nutrients ( particularly phosphorus ) from the earth ; in exchange , the fungus receives <unk> from <unk> . In North America , associations with oak and pine are usual , while in India , it has been noted to grow commonly with <unk> pine ( Pinus <unk> ) and <unk> ( <unk> <unk> ) . The false earthstar is found on the ground in open fields , often scattered or in groups , especially in nutrient @-@ poor , sandy or <unk> soils . It has also been reported to grow on rocks , preferring acid substrates like slate and granite , while avoiding substrates rich in lime . In Nepal , fruit bodies have been collected at elevations of 3 @,@ 000 m ( 9 @,@ 800 ft ) . Fruit bodies typically appear in autumn , although the dry fruit bodies are persistent and may last up to several years . <unk> <unk> is a <unk> fungus with minute , gelatinous , <unk> ( cushion @-@ shaped ) <unk> , known to grow only on the inner surface of the rays of dead Astraeus species , including A. hygrometricus . 
 The species has a cosmopolitan distribution except for <unk> , alpine and cold temperate regions ; it is common in temperate and tropical regions of the world . It has been collected in Africa , Asia , Australia , Europe , North America , and South America . 
 
 = = <unk> compounds = = 
 
 Mushroom <unk> from a number of species have attracted research interest for their <unk> and <unk> properties . <unk> from A. hygrometricus containing the <unk> named AE2 were found to inhibit the growth of several tumor cell lines in laboratory tests , and stimulated the growth of <unk> , <unk> , and bone marrow cells from mice . The extract also stimulated mouse cells associated with the immune system ; specifically , it enhanced the activity of mouse natural killer cells , stimulated macrophages to produce nitric oxide , and enhanced production of <unk> . The activation of macrophages by AE2 might be mediated by a <unk> @-@ activated protein kinase pathway of signal transduction . AE2 is made of the simple <unk> <unk> , glucose , and <unk> in a 1 : 2 : 1 ratio . 
 In addition to the previously known steroid compounds <unk> @-@ 7 @,@ 22 @-@ <unk> @-@ 3 @-@ <unk> acetate and <unk> @-@ <unk> ( 14 ) , 22 @-@ <unk> @-@ 3 @-@ one , three unique <unk> — derivatives of 3 @-@ <unk> @-@ <unk> — have been isolated from fruit bodies of A. hygrometricus . The compounds , named <unk> , 3 @-@ <unk> @-@ <unk> , and <unk> ( 3 @-@ <unk> @-@ <unk> @-@ <unk> @-@ 8 @-@ <unk> @-@ 26 @,@ 22 @-@ lactone ) , have <unk> @-@ lactone ( a six @-@ membered ring ) in the side chain — a chemical feature previously unknown in the <unk> . A previously unknown <unk> <unk> ( <unk> , <unk> @-@ <unk> ( <unk> , <unk> ) <unk> @-@ 7 @,@ 22 @-@ <unk> @-@ <unk> @-@ <unk> <unk> ) has been isolated from mycelia grown in liquid culture . The compound has a <unk> <unk> @-@ type nucleus . 
 <unk> <unk> of the fruit body are high in <unk> activity , and have been shown in laboratory tests to have anti @-@ inflammatory activity comparable to the drug <unk> . Studies with mouse models have also demonstrated <unk> ( liver @-@ protecting ) ability , possibly by restoring diminished levels of the <unk> enzymes <unk> <unk> and <unk> caused by experimental exposure to the liver @-@ damaging chemical carbon <unk> . 
 
 = = Traditional beliefs = = 
 
 This earthstar has been used in traditional Chinese medicine as a <unk> agent ; the spore dust is applied <unk> to stop wound bleeding and reduce <unk> . Two Indian forest tribes , the <unk> and the <unk> of <unk> Pradesh , have been reported to use the fruit bodies <unk> . The spore mass is blended with <unk> seed oil , and used as a <unk> against burns . The Blackfoot of North America called the fungus " fallen stars " , considering them to be stars fallen to the earth during supernatural events . 
 
 