CLASSIFICATION
(SOURCE: NCBI database)

KINGDOM: Fungi
DIVISIONS:Nearly all the Glomeromycota, and large parts of the Ascomycota and Basidiomycota; About 10% of all identified fungal species are capable of forming mycorrhiza.

MYCORRHIZA
diagram cross-section of root with ectomycorrhiza, a form of mycorrhiza

From classical Greek, myco means "fungus," and rhiza means "root." Therefore, the word mycorrhiza literally means "fungus-root." When hyphae of certain fungi form specialized sheaths around the roots of certain plants, that fungal root-coating is the mycorrhiza. In the picture of the pine-tree roots at the right, the thicker root is covered with mycorrhiza while the slender root isn't.

Roots covered with mycorrhiza improve many plants' ability to survive droughts, to acquire mineral nutrients, to store carbohydrates, and more.

cross section of root showing ectomycorrhiza, a kind of mycorrhiza

The drawing at the left shows a cross section of a root with mycorrhiza. The fungal sheath, which constitutes the main body of a mycorrhiza, is a mass of hyphae encasing the root. Filaments of hyphae growing away from the root provide the mycorrhiza more surface area for absorbing water and nutrients.

Mycorrhizae usually are divided into two main types:

ECTOMYCORRHIZAE, whose cells do not penetrate a root's cell walls and enter the cells (as in the drawing). Tree species with ectomycorrhizae include pine, oak, beech, spruce, maple, juniper, willow and elm.

ENDOMYCORRHIZAE, whose cells do penetrate the root's cell walls and enter the cells. Plants with endomycorrhizae include the legumes, grasses, tomatoes, apples, strawberries and peaches.

Mycorrhizae on roots of European Oak seedling in Germany; image courtesy of Wilhelm Zimmerling and Wikimedia Commons Mycorrhizae on roots of European Oak seedling, Quercus robur, in Germany; image courtesy of Wilhelm Zimmerling and Wikimedia Commons

Though some plants can't survive without mycorrhiza -- certain orchid species, for instance -- most can get along without it. Mycorrhizae simply improve their ability to survive. The hyphae of many kinds of fungus, including some of our most common mushroom producers, form mycorrhizae. Some fungus species form mycorrhizae on the roots of a broad range of plant species, while others "infect" only a few. Similarly, some plants can have any of several fungus species forming mycorrhiza on their roots. Douglas Firs form mutually helpful (symbiotic) relationships with around 2000 fungal species!

OTHER AMAZING MYCORRHIZA FACTS

Here are some specific ways in which mycorrhizae help plants:

MYCORRHIZA SOCIALISM

In the early 1990s mycologist Suzanne Simard and her team at Oregon State University discovered that cobwebby networks of mycorrhiza could connect not only many trees of the same species but also trees of different species. They encountered birch connected to fir trees by up to ten different species of fungi. Moreover, birch trees growing in bright sunlight seemed to be subsidizing fir trees in the shade by sharing sugars via their mycorrhizal network.

  • Ectomycorrhizae can interconnect different host plants: When mycorrhizal hyphae from different host plants meet as they travel through the soil -- even if they're from different host-plant species -- often they fuse, so that a flow of carbohydrates and other nutrients can move from one mycorrhizal system into another, and even from one host plant to another. A dominant tree, then, by way of the network of fused mycorrhizal hyphae below it, may provide nutrients to tree seedlings, shrubs and herbs in its shade, thus diversifying and enriching the local ecosystem.