SUMMARY
Sporophores of a small Fomes sp. from living giant cactus (Cereus gigantens) and some large, living chollas (Opuntia spp.) were studied and compared with Fomes sporophores from several other woody plants in the dry areas of southwestern United States. From morphological and cultural characters it was found to be closely related to Fomes robustus Karst., although sporophores were smaller and more rimose.
Sporophores from several associated desert shrubs and small trees other than cacti were found to be the same fungus. Fomes texanus from Juniperus is morphologically very similar to F. robustus but differs culturally from this form in its slower growth. F. arctostaphyli, which is another small species in the West, differs culturally and morphologically from F. robustus and is also culturally distinct from the large and somewhat closely related species F. igniarius.