About Hygrophoropsis rufa (D.A.Reid) Knudsen
The fruit body of Hygrophoropsis rufa has an orange to dark brown cap that can grow up to 10 cm (4 in) across. Its stipe, flesh, and decurrent gills are all orange, and the gills are forked. This species can produce a penetrating, ozone-like smell, which has been reported to resemble the scent of the orchid Oncidium ornithorhynchum or a photocopier. The spores of Hygrophoropsis rufa are thick-walled, ellipsoid in shape, and measure 5.6–6.4 by 3.6–4.4 micrometres (μm). Spores give a strongly dextrinoid reddish-brown staining reaction when tested with Melzer's reagent, though not all spores will react. When examined microscopically, the cap cuticle cells form a trichoderm: the outermost hyphae emerge roughly parallel to each other, like hairs, and grow perpendicular to the surface of the cap. These hyphae fall into three categories: broad, thick-walled, and hyaline (translucent); filiform (threadlike); or containing granular golden-brown contents. This cap structure differs from the closely related Hygrophoropsis aurantiaca, which has a cap cuticle arranged as a uniformly tangled cutis with hyphae parallel to the cap (pileus) surface. Hygrophoropsis rufa is a rare saprophytic fungus that fruits on woodchips or close to conifer stumps. Confirmed records of the species come from the United Kingdom, Austria, Germany, and Denmark; unconfirmed internet photographs suggest it may have a wider distribution that includes France and Slovakia.
