Cortinarius cinnamomeus colonizes the root systems of the sedges Carex flacca and Carex pilulifera, forming ectomycorrhizal-like structures lacking a Hartig net—a network of hyphae that penetrate between the epidermal and cortical cells of the root.
Carex | Carex sylvatica | Carex nigra | Carex lyngbyei | Carex leporina | Carex geyeri | Carex flacca | Carex echinata | The fungus forms ectomycorrhiza-like structures with the sedge ''Carex flacca | Carex utriculata | Carex rossii | Carex pilulifera | Carex otrubae | Carex inops | Carex emoryi | ''Carex binervis'' in its typical habitat, growing among ''Calluna |
The larvae overwinter and feed on various grasses, including glaucous sedge and cock's-foot.