<p>Mycorrhiza is a symbiotic association between plant root and fungus, contributing to plant mineral nutrition and defence against antagonists. The mycorrhizal collaboration niche characterizes the position of plant species along a gradient of reliance on mycorrhiza. In this Perspective, we introduce the plant mycorrhizal traits that describe these niches and explore upscaling them to describe community-scale and macroecological-scale structure, including relationships with ecosystem function. Plant mycorrhizal type, status, dependency and root colonization rate characterize mycorrhizal niche optima, whereas flexibility and variation of root colonization rate, indicating the plasticity of plants in their reliance on mycorrhiza, describe mycorrhizal niche width. Abundance-weighted community means of plant mycorrhizal traits offer a way of upscaling trait information and examining mycorrhizal niche structure across communities and biomes. An illustrative analysis indicated that the share of highly mycorrhiza-reliant plant species decreases in biomes of more recent biogeographic origin at high latitudes. Arbuscular mycorrhizal plants become less prevalent, and those remaining tend to be flexible. The highest overall flexibility is observed in anthropogenic semi-natural grasslands, whereas, contrastingly, natural grasslands exhibit low overall mycorrhizal flexibility. Further advances in the field will be underpinned by the development of standardized approaches for measuring mycorrhizal traits.</p>