This is microscopically and macroscopically impossible to tell from Exidia glandulosa except by its substrate. E. glandulosa is almost always on oak or hazel. Exidia plana is on other hardwoods but not, apparently, on oak. E. glandulosa is often more turbinate and leaflike while E. plana is often more spreading and effused; but in practice hard to separate in those terms. Both are called "Witches' butter".