[er·ə¦kā·shəs ‚mī·kə¦rīz·əl ′fən·jī] (mycology) Mycorrhizal fungi that form symbiotic relationships with plants in the Ericaceae family; they are divided into three subgroups based on the presence or absence of a Hartig net, a fungal sheath, and fungal hyphae within the root cells.