The Order Geosiphonales is a taxonomic group within the phylum Glomeromycota, class Glomeromycetes, encompassing fungi that form unique symbiotic relationships with cyanobacteria. Unlike typical arbuscular mycorrhizal fungi, members of this order, such as Geosiphon pyriformis, establish intracellular associations with cyanobacteria, notably Nostoc, within specialized structures known as bladders. These bladders, which protrude from the soil surface, house the cyanobacteria and are involved in nutrient exchange, with the cyanobacteria providing fixed nitrogen to the host fungus. This symbiosis is considered more analogous to mycorrhizal relationships than to lichen associations, as it involves an intracellular rather than an extracellular partnership. The Geosiphon-Nostoc symbiosis is notable for its ecological role in nitrogen cycling and its distinctive morphological and physiological characteristics within the fungal kingdom.