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''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 unopened. 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 micrometers in diameter. Despite a similar overall appearance, ''A. hygrometricus'' is not related to the true earthstars of genus ''Geastrum'', although historically, they have been taxonomically confused. The species was first described by Christiaan Hendrik 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 bioactive 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 Hendrik Persoon in 1801〔 (as ''Geaster'', 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 capillitium threads, not having a true hymenium, and having larger spores. Accordingly, Morgan set Persoon's ''Geaster hygrometricum'' 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 Herriot Cunningham explicitly transferred the species back to the genus ''Geastrum'' in 1944, explaining: The treatment of this species by certain taxonomists well illustrates the pitfalls that lie in wait for those who worship at the shrine of ontogenic 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 glebal cavities are separated by tramal plates so tenuous as to be overlooked by the uncritical 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 fructification of any other member of the genus. The taxonomist 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 taxonomical authority MycoBank,〔 synonyms of ''Astraeus hygrometricus'' include ''Lycoperdon stellatus'' Scop. (1772);〔 ''Geastrum fibrillosum'' Schwein. (1822);〔 ''Geastrum stellatum'' (Scop.) Wettst. (1885); and ''Astraeus stellatus'' E.Fisch. (1900).〔 ''Astraeus hygrometricus'' has been given a number of colloquial names that allude to its hygroscopic behavior, including the "hygrometer 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 ὑγρός (''hygros'') "wet" and μέτρον (''metron'') "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 macroscopic and microscopic characteristics.〔 Molecular studies of the DNA sequences of the ITS 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 Petcharat's ''A. thailandicus'' 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 phylotypes, 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 V.J. Stanĕk in 1958;〔 it was later (1976) published as a distinct species—''A. koreanus''—by Hanns Kreisel.〔 As pointed out by Fangfuk 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.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Astraeus hygrometricus」の詳細全文を読む スポンサード リンク
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