Unfortunately there are a number of genera of these flat, white fungi on wood and many are indistinguishable to the naked eye. They are quite diverse in the microscopic structures and these are used to identify genus.
Possibly the asexual state of a species of Botryobasidium. An asexual reproducing form and the sexual reproducing form of a given fungus are often markedly different visually. For many species the forms were assigned to different genera during the long time before it was possible to show that what were thought to be markedly different fungi were simply different forms of the same fungus. In those days the asexual states of Botryobasidium were assigned to the genus Haplotrichum.