Kingdom:   Fungi
Division:    Basidiomycota
Class:        Basidiomycetes
Order:       Agaricales
Family:      Schizophyllaceae
Genus:      Schizophyllum
Species:     S. commune
Binomial name: Schizophyllum commune
Synonyms:  Agaricus alneus, Agaricus alneus, Agaricus multifidus, Apus alneus, Merulius alneus, Merulius alneus,Merulius communis, Schizophyllum alneum, Schizophyllum alneum, Schizophyllum commune var. multifidum, Schizophyllum multifidum.
Common name: Split Gill.

Schizophyllum commune is common species of mushroom and is the world's most widely distributed mushroom, occurring on every continent except Antarctica where there is no wood to be used as a substrate. It is found predominantly from autumn to spring on dead wood in coniferous and deciduous forests.
The greyish white and up to 4 cm in diameter cap is shell-shaped and the gills concentrated at the point of attachment. The cap can be wavy and lobed, with a rigid margin when old.
The gills appear to be split because they can dry out and rehydrate and thus open and close many times over the course of a growing season. The mycelium only has to produce one set of fruiting bodies per year but since they can dry out and rehydrate they keep functioning.
Schizophyllum commune is a wood decay fungus that causes a white rot and it has been known to cause a human mycosis in a few cases involving immunocompetent people, especially children. In one case, the fungus had grown through the soft palate of a child's mouth and was actually forming fruiting bodies in her sinuses.

The link is to an article on fungal sinusitis in humans. http://www.hindawi.com/journals/criid/2011/821259/   

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Schizophyllum commune
Split-gill mushroom Schizophyllum commune-001.jpg

Split-gill mushroom Schizophyllum commune 3.JPG

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Photo showing the split gills
Schizophyllum commune-001.JPG

There is a small red thrip in the gills.
Schizophyllum commune-001.JPG

Thanks to Wikipedia for text and information: https://creativecommons.org/licenses/by-sa/3.0/