Sac fungi, or ascomycetes, are a group of fungi most of which possess sacs, or asci, in which spores are produced. The relatively common blue-green cup fungi, Chlorociboria aeruginascens and its close relative, Chlorociboria aeruginosa, are in this group and are referred to as Green Stain Fungi (as well as Green Elfcup or Green Wood Cup). Most of the time you do not see the actual fruiting bodies of these fungi. More often you come across the brilliantly blue-green stained wood (often rotting logs of poplar, aspen, ash and oak) for which these fungi are responsible. Woodworkers call this wood “green rot” or “green stain.” 14th and 15th century Italian Renaissance woodworkers used Chlorociboria-infected wood to provide the green colors in their intricate wood inlays. The blue-green discoloration is caused by the production of the pigment xylindein, which may make wood less appealing to termites and has been studied for its cancer-fighting properties.
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