The glomeromycetes are obligate symbiotic fungi forming arbuscular mycorrhizae with the roots or thalli (e.g. in bryophytes) of land plants. At present, it is impossible to establish culture of glomeromycetes without plant. The arbuscular mycorrhizae are found in most land plants, and glomeromycetes contribute largely to terrestrial ecosystem. Land plants give organic matter to glomeromycetes which help plants to absorb water and nutrients from soil and to enlarge disease resistance of plants. This mutual relationship sometimes changes to the damage to plants or the parasitism on fungi. A unique representative, Geosiphon forms an endocytobiotic association with cyanobacteria (Nostoc)

The glomeromycetes have coenocytic hyphae, thus they were classified into the 'Zygomycota'. The hyphae invade intracellular space (between cell wall and cell membrane) of plant and form highly branched structures for nutrient exchange with plant, arbuscules. Some species also form strage structures, vesicles (e.g. Glomus). They reproduce asexually through blastic development of the hyphal tip to produce large spores (glomerospores; sometimes reach to 800 µm) inside or outside of roots. The glomerospore enclosed by multilayered cell wall includes many nuclei. Sexual reproduction is unknown.