The useful functional association between fungi and the roots of higher plants is called mycorrhiza. Mycorrhiza is a symbiotic relationship between fungi and plant roots, where both organisms benefit. The fungi form a network of hyphae that colonize the roots of the plants, creating a mutually beneficial relationship.

In mycorrhizal associations, the fungi provide several benefits to the plants. They enhance the plant`s ability to absorb water and nutrients from the soil, particularly phosphorus and nitrogen. The extensive network of fungal hyphae increases the surface area of the plant roots, allowing for more efficient nutrient uptake. In return, the plant provides the fungi with carbohydrates and other organic compounds produced through photosynthesis.

Mycorrhizal associations are crucial for the growth and survival of many plant species, especially in nutrient-deficient soils. They play a significant role in enhancing plant nutrient uptake, improving soil structure, and promoting plant growth. Therefore, mycorrhiza is a useful functional association between fungi and the roots of higher plants.