also called vesicular-arbuscular mycorrhizae (VAM)
fungus does not form a sheath around the roots--fungus penetrates the cortical cells, but does not penetrate the cell membrane
fungus is a member of Zygomycota
more common than ectomycorrhizae
Endomycorrhizae form with about 0% of plants in nature, including all the grasses (but not sedges, which usually lack mycorrhizae) ,most herbacesous plants, and some trees.