A book from Paul Stamets, 1993 (Growing gourmet and medicinal mushrooms) lists both Hypsizygus ulmarius and H. tessulatus as saprophytes. It can also be a facultative parasite on dying hardwoods or a true saprophyte on dead trees. I feel we humans try to label organisms, but the organisms sometimes fit inbetween different labels, depending on the situation. Peter Oei