Tremella globosporaReid is described from 32 collections made in British Columbia. The fungus grows directly from within perithecia of species ofValsaandDiaporthefound, in this study, on hosts belonging to seven Angiosperm genera and three of Gymnosperm. Single-spore isolates were made from basidiocarps selected to represent as many variables as possible; both colors (yellow and white) of the basidiocarp, proximity of position on a single twig versus considerable distance between sites, both genera of pyrenomycete host, four genera of seed plants, and collection dates from January to September. Compatibility tests indicated a single species with a modified tetrapolar mating system typical of the genusTremella. Selected dikaryotic isolates were grown in laboratory culture on simple media, and fertile basidiocarps were produced. Variation in size, color, and consistency of basidiocarps in culture was compared with those in field collections. Clamp connections, branching from the clamp cell, and other microstructures produced in culture are also described. No reaction ofT. globosporatoValsacultures or sterilizedValsaperithecia and extracts was observed.