Figure 17.3 Mycorrhizal fungi. Mycorrhizal fungi can be categorized as endomycorrhizal fungi or ectomycorrhizal fungi. (a) Endomycorrhizal fungi have hyphae that penetrate the root cells of plants and reside between the cell wall and cell membrane. (b) Ectomycorrhizal fungi have hyphae that do not penetrate the root cells but instead grow between the root cells of plants.