We don't usually see the fruiting stage of Chlorociboria aeruginacens, a common fungus that inhabits rotting wood, and oak in particular. The blue-green barkless tree debris we encounter on our walks is not discarded painted wood (as I used to think), but is caused by the mycelium penetrating and staining the substrate. The small stalked cup-shaped fruiting body is almost an 'unreal' turquoise color.