A molecular guide to the taxonomy of arbuscular mycorrhizal fungi.

In this issue of New Phytologist, Krüger et al. (pp. 970–984) present an extensive molecular phylogeny of arbuscular mycorrhizal fungi (AMF). This is the basis for a radical modernization of the taxonomy and will be an important point of reference for future studies. Sift through any soil in which plants have grown, and there is a good chance that it will contain the spores of AMF. It requires a careful eye to spot them, though, as even the largest, the ‘giant spores’ of Gigaspora gigantea, are less than half a millimetre across (Fig. 1). The other parts of the fungus are even less conspicuous: a gossamer web of hyphae spreading through the soil, and structures within plant roots that are only visible under the microscope. Unsurprisingly, the identification of AMF is challenging, but it is important because AMF form symbioses with the majority of land plants. They have major effects on plant growth in a number of ways, the best known being by aiding phosphorus uptake (Smith & Read, 2008).