Editing Secotioid (section)

==Explanation of secotioid development and gasteromycetation==

Historically [[agarics]] and [[boletes]] (which bear their spores on a [[hymenium]] of gills or tubes respectively) were classified quite separately from the [[gasteroid fungi]], such as [[puff-balls]] and [[truffles]], of which the spores are formed in a large mass enclosed in an outer skin.  However, in spite of this apparently very great difference in form, recent mycological research, both at microscopic<ref name=thiers/> and molecular<ref name=Hibbett/> level has shown that sometimes species of open mushrooms are much more closely related to particular species of gasteroid fungi than they are to each other.  Fungi which do not open up to let their spores be dispersed in the air, but which show a clear [[Morphology (biology)|morphological]] relation to agarics or boletes, constitute an intermediate form and are called '''secotioid'''.<ref name=thiers/>

The word is derived from the name of the genus ''[[Secotium]]'', which was defined in 1840 by [[Gustav Kunze|Kunze]] for a South African example, ''S. gueinzii'', which is the type species.  In the following years numerous secotioid species were added to this genus, including ones which according to modern taxonomy belong to other genera or families.<ref name=Conard/><ref name=SFSecotium/><ref name=IFSecotium/>

On a microscopic scale, secotioid fungi do not expel their spores forcibly from the basidium; their spores are "statismospores".  Like gasteroid fungi, secotioid species rely on animals such as rodents or insects to distribute their spores.

It can at times be disadvantageous for a mushroom to open up and free its spores in the usual way.  If this development is aborted, a secotioid form arises, perhaps to be followed eventually by an evolutionary progression to a fully gasteroid form.  This type of progression is called '''gasteromycetation''' and seems to have happened several times independently starting from various genera of "normal" mushrooms.  This means that the secotioid and also the gasteroid fungi are [[polyphyletic]].  According to the paper by Thiers,<ref name=thiers/> in certain climates and certain seasons, it may be an advantage to remain closed, because moisture can be conserved in that way.

[[File:Brockhaus and Efron Encyclopedic Dictionary b11 168-5.jpg|thumb|130px|left|Cross-section of ''Hymenogaster tener'']]
For example, the gasteroid genus ''[[Hymenogaster]]'' has been shown to be closely related to agaric genera such as ''[[Hebeloma]]'', which were formerly placed in family [[Cortinariaceae]] or [[Strophariaceae]].  This is found by DNA analysis and also indicated on a microscopic scale by the resemblance of the spores and basidia.  According to a current classification system, ''Hebeloma'' now belongs to family [[Hymenogastraceae]], and is considered more narrowly related to the closed ''[[Hymenogaster]]'' fungi than, for instance, to the ordinary mushrooms in genus ''[[Cortinarius]]''.<ref name=Binder/><ref name=Francis/>

A similar case is the well-known "Deceiver" mushroom ''[[Laccaria laccata]]'' which is now classified in the ''[[Hydnangiaceae]]'', ''Hydnangium'' being a gasteroid genus.

It has been found that a change in a single locus of a gene of the gilled mushroom ''[[Lentinus tigrinus]]'' causes it to have a closed fruiting body.  This suggests that the emergence of a secotioid species may not require many mutations.<ref name=Hibbett/>

There is a spectrum of secotioid species ranging from the open form to the closed form in the following respects:
*there may be an evident stipe, or there may be only a remnant consisting of a column of non-fertile tissue,
*if there is a stipe the edge of the cap may separate from it (partially opening), or may not,
*there may be recognizable gills (though oriented in all directions and very convoluted), or the fertile interior may be uniform like the [[gleba]] of gasteroid fungi, and
*the spore-bearing tissue may be above ground ([[epigeous]]), or underground ([[wikt:hypogeous|hypogeous]]), or partly buried.

The adjective "'''sequestrate'''" is sometimes used as a general term to mean "either secotioid or gasteroid".