Arbuscular mycorrhizal fungi (AMF) have recently been reclassified into a new Phylum called Glomeromycota (SchuBler et al., 2001). The fungal members of this Phylum are obligated symbionts and potentially AMF-forming. This Phylum also includes Geosiphon pyriforme, which forms mutualistic symbiosis with the cyanobacteria Nostoc.
The fungi belonging to the Phylum Glomeromycota are characterized by non-septed mycelium, and do not reproduced sexually. Spores are asexual, large, and are surrounded by a thick cell wall that is formed by several layers. Spores germinate in soil, and the germinative tube grows either directly from inside crossing the cell wall or by internal specialized structures.
The Phylum Glomeromycota includes four Orders, five Families, and aproximately seven well defined Genera (three more in the process of being named). There are aproximately 150 different species of fungi, which are able to form AMF-symbiosis with higher plants.
For further information about the taxonomy of AMF, please review the following paper: