Ectomycorrhiza, or
ectotrophic mycorrhizae, is a
symbiotic relationship between a
fungus and the roots of a plant. The
fungus forms a
sheath around the root, extending thin
filaments called
hyphae into the soil and into the
root itself.
It can be harmful to the host plant, or benefit the host by bringing more nitrogen and other nutrients into the roots. Ectotrophic mycorrhizae occur more often in forest soils.