''Astraeus'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

fungi A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...

in the family Diplocystaceae. The genus, which has a

cosmopolitan distribution In biogeography, a cosmopolitan distribution is the range of a taxon that extends across most or all of the surface of the Earth, in appropriate habitats; most cosmopolitan species are known to be highly adaptable to a range of climatic and en ...

, contains nine species of earthstar mushroom. They are distinguished by the outer layer of flesh ( exoperidium) that at maturity splits open in a star-shape manner to reveal a round

spore In biology, a spore is a unit of sexual reproduction, sexual (in fungi) or asexual reproduction that may be adapted for biological dispersal, dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores fo ...

sac. Additionally, they have a strongly

hygroscopic Hygroscopy is the phenomenon of attracting and holding water molecules via either absorption (chemistry), absorption or adsorption from the surrounding Natural environment, environment, which is usually at normal or room temperature. If water mol ...

character—the rays will open when moist, but when hot and dry will close to protect the spore sac. Species of ''Astraeus'' grow on the ground in

ectomycorrhizal An ectomycorrhiza (from Greek ἐκτός ', "outside", μύκης ', "fungus", and ῥίζα ', "root"; ectomycorrhizas or ectomycorrhizae, abbreviated EcM) is a form of symbiotic relationship that occurs between a fungal symbiont, or mycobion ...

associations with trees and shrubs. Despite their similar appearance to the ''

Geastrum ''Geastrum'' (orthographical variant ''Geaster'') is a genus of puffball-like mushrooms in the family Geastraceae. Many species are commonly known as earthstars. The name, which comes from ''geo'' meaning ''earth'' and meaning ''star'', refers ...

'' earthstars, the species of ''Astraeus'' are not closely related.

Description

The

mycelium Mycelium (: mycelia) is a root-like structure of a fungus consisting of a mass of branching, thread-like hyphae. Its normal form is that of branched, slender, entangled, anastomosing, hyaline threads. Fungal colonies composed of mycelium are fo ...

of immature specimens is fibrous, and originates from all parts of the surface. The

peridium The peridium is the protective layer that encloses a mass of spores in fungi. This outer covering is a distinctive feature of gasteroid fungi. Description Depending on the species, the peridium may vary from being paper-thin to thick and rubb ...

is roughly spherical, and made of two distinct tissue layers. The outer layer, the exoperidium, is thick, leathery, and initially inseparable from the inner layer (endoperidium). At maturity, the exoperidium bursts open into several pointed "rays". The inner layer of tissue, the endoperidium, is thin, like a membrane. The spore case enclosed by the endoperidium has no stalk ( sessile), and is opened at the top by a tear or pore. Microscopically, sterile cells, long-threaded cells called capillitium originate from the inner surface of the peridium; they are highly branched and interwoven. The

s are large, spherical, minutely warted, and brown. ''Astraeus'' species are strongly

, and absorb moisture from the environment, so that the rays are closed over the spore case when dry, but open up flat when moistened.

History

The genus ''Astraeus'' was first described by the American mycologist and botanist Andrew Price Morgan in 1885. The outward resemblance of ''Astraeus'' species with those from genus '' Geaster'' (family

Geastraceae Geastrales is an order of gasterocarpic basidiomycetes (fungi) that are related to Gomphales. The order contains the families Geastraceae, which includes the "earthstars" formerly placed in Lycoperdales or Phallales, and also Schenellaceae, Sc ...

) has led several authors to place them in that genus. Phylogenetic analyses proved that the genus ''Astraeus'' together with the genera '' Boletinellus'', '' Phlebopus'', '' Pisolithus'', ''

Calostoma ''Calostoma'' is a genus of 29 species of gasteroid fungi in the suborder Sclerodermatineae. Like other gasteroid fungi, ''Calostoma'' do not have the spore discharge mechanism associated with typical gilled fungi ( ballistospory), and instead ...

'', ''

Gyroporus The Gyroporaceae are a family (biology), family of fungi in the order Boletales. The family is monogeneric, containing the single genus ''Gyroporus'', which, according to a 2008 estimate, contains ten widely distributed species, though a more rec ...

'', ''

Scleroderma Scleroderma is a group of autoimmune diseases that may result in changes to the skin, blood vessels, muscles, and internal organs. The disease can be either localized to the skin or involve other organs, as well. Symptoms may include areas ...

'', and '' Veligaster'', form a distinct phylogenetic lineage in the

Boletales The Boletales are an order of Agaricomycetes containing over 1300 species with a diverse array of fruiting body types. The boletes are the best known members of this group, and until recently, the Boletales were thought to only contain boletes. ...

; these genera collectively form the suborder

Sclerodermatineae Sclerodermatineae is a suborder of the fungal order Boletales. Circumscribed in 2002 by mycologists Manfred Binder and Andreas Bresinsky, it contains nine genera and about 80 species. The suborder contains a diverse assemblage fruit body morpho ...

. The similarity between ''Geastrum'' and ''Astraeus'' species is an example of

convergent evolution Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last comm ...

. ''Astraeus'' is currently classified in the family Diplocystaceae.

Species

For a long time, the genus ''Astraeus'' was thought to contain at most two species. However, studies in the 2000s showed that species collected from around the world and labelled under the

specific epithet In Taxonomy (biology), taxonomy, binomial nomenclature ("two-term naming system"), also called binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin gramm ...

''hygrometricus'' were actually considerably variable in a number of

macroscopic The macroscopic scale is the length scale on which objects or phenomena are large enough to be visible with the naked eye, without magnifying optical instruments. It is the opposite of microscopic. Overview When applied to physical phenome ...

and

microscopic The microscopic scale () is the scale of objects and events smaller than those that can easily be seen by the naked eye, requiring a lens or microscope to see them clearly. In physics, the microscopic scale is sometimes regarded as the scale betwe ...

characteristics. A

molecular A molecule is a group of two or more atoms that are held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemistry, ...

study of the

DNA sequence A nucleic acid sequence is a succession of bases within the nucleotides forming alleles within a DNA (using GACT) or RNA (GACU) molecule. This succession is denoted by a series of a set of five different letters that indicate the order of the nu ...

s of the ITS region of the

ribosomal DNA The ribosomal DNA (rDNA) consists of a group of ribosomal RNA encoding genes and related regulatory elements, and is widespread in similar configuration in all domains of life. The ribosomal DNA encodes the non-coding ribosomal RNA, integral struc ...

from a number of ''Astraeus'' specimens from around the world has helped to establish the

phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...

relationships within the genus. Currently, eight species are recognized: * '' Astraeus asiaticus'' Phosri, M.P. Martín & Watling : This species, thought to be an Asian version of ''A. hygrometricus'', is found in the northern areas of Thailand. Its

gleba Gleba (, from Latin ''glaeba, glēba'', "lump") is the fleshy spore-bearing inner mass of certain fungi such as the puffball or stinkhorn. The gleba is a solid mass of spores, generated within an enclosed area within the sporocarp. The conti ...

has a purplish-chestnut color when mature, and a granulate outer peridium. The range of its spore sizes are generally larger than ''A. hygrometricus'' (upper diameter of 15.2

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

). * ''

Astraeus hygrometricus ''Astraeus hygrometricus'', commonly known as the hygroscopic earthstar, the barometer earthstar, or the false earthstar, is a species of fungus in the family Diplocystaceae. Young specimens resemble a puffball when unopened. In maturity, the ...

'' (Pers.) Morgan * '' Astraeus koreanus'' (V.J.Staněk) Kreisel *'' Astraeus morganii'' Phosri, Watling & M.P.Martín * '' Astraeus odoratus'' Phosri, Watling, M.P.Martín & Whalley : Discovered in

Thailand Thailand, officially the Kingdom of Thailand and historically known as Siam (the official name until 1939), is a country in Southeast Asia on the Mainland Southeast Asia, Indochinese Peninsula. With a population of almost 66 million, it spa ...

, fresh species have a strong odor, and a smooth outer surface. * '' Astraeus pteridis'' (Shear) Zeller *'' Astraeus sirindhorniae'' Watling, Phosri, Sihanonth, A.W.Wilson & M.P.Martín *'' Astraeus smithii'' Watling, M.P.Martín & Phosri *'' Astraeus telleriae'' M.P.Martín, Phosri & Watling

Bioactive compounds

In 2008, five lanostane-type

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

s were isolated and identified from the fruit bodies of ''A. pteridis''; two of these compounds had an inhibitory effect on the growth of the pathogen ''

Mycobacterium tuberculosis ''Mycobacterium tuberculosis'' (M. tb), also known as Koch's bacillus, is a species of pathogenic bacteria in the family Mycobacteriaceae and the causative agent of tuberculosis. First discovered in 1882 by Robert Koch, ''M. tuberculosis'' ha ...

''.

References

{{Taxonbar, from=Q10420904 Boletales Boletales genera