The fungal species responsible for the formation of vesicular-arbuscular mycorrhizae (VAM) have been placed in four of the genera in the Endogonaceae, an ancient group which has Devonian fossil representatives. Nine genera are recognized in the Endogonaceae: Acaulospora, Endogone, Gigaspora, Glaziella, Glomus, Modicella, Sclerocystis, Complexipes, and Entrophospora. Chlamydospores are formed in hypogeous or epigeous sporocarps, in sporocarps on twigs or leaves in the litter layer, singly in the soil, or in the cortex of roots. As in Gigaspora, the "azygospores" are formed singly and ectocarpically in the soil. Chlamydospores are formed similar to those produced by Glomus, but are invariably formed in tight sporocarps with the spores arranged in a single layer around a central plexus of glebal hyphae. The mode of formation and development of the zygospores parallels that in other members of the Mucorales. Both species in modicella genus produce sporangiospores in thin-walled terminal sporangia formed in sporocarps.