Scutellospora rubra is a new arbuscular mycorrhizal species trapped in a pot culture of rhizosphere soil from Eucalyptus dunnii. Spores are dark red-brown 140-220 µm diam., and closely resemble those of S. heterogama in size, colour, and subcellular organization, but the outer layer of the spore wall is smooth rather than ornamented. Resolution of such species-level variation to properties of the spore wall is consistent with that measured among all other species of arbuscular mycorrhizal fungi studied to date.