Tremella mesenterica (common names include yellow brain, golden jelly fungus, yellow trembler, and witches' butter) is a common jelly fungus in the family Tremellaceae of the Agaricomycotina. It is most frequently found on dead but attached and on recently fallen branches, especially of angiosperms, as a parasite of wood decay fungi in the genus Peniophora. The gelatinous, orange-yellow fruit body of the fungus, which can grow up to 7.5 cm (3.0 in) diameter, has a convoluted or lobed surface that is greasy or slimy when damp. It grows in crevices in bark, appearing during rainy weather. Within a few days after rain it dries into a thin film or shriveled mass capable of reviving after subsequent rain. This fungus occurs widely in deciduous and mixed forests and is widely distributed in temp