The anatomy of vesicular-arbuscular mycorrhizas formed by 10 species from the Endogonaceae within subterranean clover roots was compared using light microscopy. In pot cultures of single species of fungi each fungus formed a characteristic infection pattern within roots of subterranean clover. Fungi from the genera Glomus (excluding G. tenuis), Acaulospora and Gigaspora were readily distinguished from each other. Within each genus, species varied in the extent to which they formed hyphae or vesicles with dissimilar morphology. Differences among genera were always greater than those among species within genera. This emphasizes a role for infection morphology in taxonomic descriptions of the fungi which are usually limited to features of spores. A key is provided to the characteristics useful for distinguishing among these 10 species of fungi within roots of subterranean clover.