Mycorrhizal symbiosis between plants and fungi is one of the most well-known plant-fungus associations and is of significant importance for plant growth and persistence in many ecosystems; over 90% of all plant species engage in mycorrhizal relationships with fungi and are dependent upon this relationship for survival.

"common mycorrhizal networks."

The mycorrhizal symbiosis is ancient, dating to at least 400 million years ago.

It often increases the plant's uptake of inorganic compounds, such as nitrate and phosphate from soils having low concentrations of these key plant nutrients. The fungal partners may also mediate plant-to-plant transfer of carbohydrates and other nutrients. Such mycorrhizal communities are called "common mycorrhizal networks."

"common mycorrhizal networks."

A special case of mycorrhiza is myco-heterotrophy, whereby the plant parasitizes the fungus, obtaining all of its nutrients from its fungal symbiont.

Monotropa uniflora parasites fungi in the family Russulaceae

In addition to mycorrhizal associations, plants are associated with fungal species called endophytes, most of which are ascomycetes.

Endophytic fungal diversity in Panama

They live within plant parts, including roots, stems, and leaves, and have been found in all plant species studied to date. Endophytes do not cause harm and, in some cases, they benefit the plant.

The slender tubes of the endophytic fungus(Neotyphodium coendophialum) in the inter-cellular spaces of tall fescue.

In non-woody plants, such as forage and turfgrasses (Festuca spp. and Lolium spp.), they may protect against environmental stresses such as heat, drought, or heavy metals. They may also improve the grasses' resistance to herbivores, including both insects and mammals.

Festuca spp.

Lolium spp

In at least one species of woody plant (the cacao tree), they have been shown to protect against pathogens.

cacao tree

The ascomycetes are a monophyletic group-- i.e., all of its members trace back to one common ancestor. This group is of particular relevance to humans as sources for medicinally important compounds, such as antibiotics and for making bread, alcoholic beverages, and cheese, but also as pathogens of humans and plants.