Molecular phylogeny, taxonomy, and evolution of Geosiphon pyriformis and arbuscular mycorrhizal fungi

Geosiphon pyriformis (Kutz.) v. Wettstein is the only known example of a fungus living in endocytobiotic association with a cyanobacterium. The close phylogenetic relationship of Geosiphon with some arbuscular mycorrhizal fungi (AMF) and the phylogenetic position of Geosiphon are shown in detail. Comprehensive small subunit (SSU) rRNA sequence analyses allow the erection of a new, molecular phylogeny-based taxonomic system for the AMF, including Geosiphon (Geosiphonaceae). Within the recently described phylum Glomeromycota (with one class, Glomeromycetes), a system including four orders was proposed. The erection of several new families will also be necessary. Evolutionary implications are discussed, referring to different possibilities of the influence of AMF on the colonization of the terrestrial habitat by plants.