Cortinarius favrei grows in the midst of dwarf birch (Betula sp.), Salix sp., Vaccinium sp., and Eriophorum sp. in the Alaskan tundra. The fruiting body (mushroom) of C. favrei is visible in the center of the photograph. When soil nitrogen is limited, most terrestrial plants develop symbiotic associations with mycorrhizal fungi. The plants receive soil nitrogen taken up the fungi, and in return the fungi receive sugars from the plants. At the Arctic LTER site, isotopic measurements indicate that mycorrhizal fungi functionally similar to C. favrei contribute 60-90% of their host plant’s nitrogen while receiving 8-16% of carbon fixed by plants during photosynthesis. This photograph originally appeared on the cover of Ecology (87:4) in April of 2006.