The primary research focus of the Harry D. Thiers Herbarium is mycology. Most of the early collections were made by Harry Thiers and his students, and later by Dennis Desjardin and his students. Specialties include fleshy fungi of North America, Hawai'i, Indonesia, and southeast Asia; California lichens, bryophytes, and flowering plants, with an exceptionally large collection of Arctostaphylos. The herbarium was established in 1959 as the SFSU Herbarium, and was renamed the HDT Herbarium following Harry's retirement in 1989.