mycorrhiza, also spelled Mycorhiza, Dr. David Midgleyan intimate association between the branched, tubular filaments (hyphae) of a fungus (kingdom Fungi) and the roots of higher plants. The association is usually of mutual benefit (symbiotic): a delicate balance between host plant and symbiont results in enhanced nutritional support for each member. The establishment and growth of certain plants (e.g., citrus, orchids, pines) is dependent on mycorrhiza; other plants survive but do not flourish without their fungal symbionts. The two main types of mycorrhiza are endotrophic, in which the fungus invades the hosts’ roots (e.g., orchids), and ectotrophic, in which the fungus forms a mantle around the smaller roots (e.g., pines). Exploitation of these natural associations can benefit forestry, horticulture, and other plant industries.