DEEMY is collecting descriptive data on ectomycorrhizae, including extant character descriptions and definitions. Ectomycorrhizae are mutualistic structures formed by fungi and the roots of forest trees. They are predominantly found in the temperate and boreal climate zones but occur also in humid tropic regions, as well as in soils of poor nutrition. Without mycorrhizae, trees would not be able to take up water and minerals. Ectomycorrhizae show a wide range of anatomical diversity which represents their possible function in tree nutrition and ecology. Their anatomical data, in general, allow a quick determination and provide at the same time ecologically important information about possible functions for tree nutrition.