Mycorrhizae are intimate, mutually beneficial associations between fungi and the roots of plants (mycorrhiza comes from the Greek word meaning "fungus-root"). All gymnosperms and approximately 80 percent of all angiosperms are thought to have naturally occurring mycorrhizal associations. The plant provides the fungus with carbohydrates made in photosynthesis, and the fungus provides the plant with increased amounts of mineral elements and water absorbed from the soil. The fungus also protects the root from pathogens.

Ectotrophic mycorrhizal fungi infecting a root. Redrawn from Taiz and Zeiger, 1998, Figure 5.10.

There are two major types of mycorrhizae, the ectomycorrhizae (also called ectotropic mycorrhizae; ecto, meaning "outside") and the endomycorrhizae (endotropic mycorrhizae; endo, meaning "inside"), that are distinguished on the basis of whether or not the fungus penetrates the root cells.

Ectomycorrhizae

In ectomycorrhizae the fungal component is usually a basidiomycete or sometimes an ascomycete. Ectomycorrhizae occur on certain groups of temperate shrubs and...