One major difference between ectomycorrhizae and arbuscular mycorrhizae is that ectomycorrhizae do not penetrate plant roots; arbuscular mycorrhizae penetrate plant roots.
This means that there is a difference how the fungus colonizes the host plant's root tissues. arbuscular mycorrhizal fungi (AMF or AM), colonizes the host plant intracellularly, while the ectomycorrhizal fungi extracellularly.