A mycorrhiza is a symbiotic association between a fungus and a plant, in which the fungus colonizes the plant's root system and helps it absorb water and nutrients from the soil, while the plant provides the fungus with organic molecules such as sugars produced by photosynthesis. The term mycorrhiza comes from the Greek words for "fungus" and "root". There are different types of mycorrhiza, depending on where the fungus grows on or inside the plant root. The most common type is the arbuscular mycorrhiza, which is found in about 70% of plant species, including many crops such as wheat and rice. Mycorrhiza play important roles in plant nutrition, soil biology, and soil chemistry, and are also involved in the evolution and ecology of plants.