Arbutoid Mycorrhizas

Arbutoid mycorrhizas are of the ect-endo type and, among the Ericaceae, are found in the genera Arbutus, Arctostaphylos and Arctous. They are also found in Pyrola of the Pyrolaceae which is also in the Ericales [N.B. Some authors recognise this as a separate type of mycorrhiza]. There is a well-developed fungal sheath and a Hartig net restricted to the outer layers of cells. Extensive penetration of the outer cortical cells occurs and hyphal coils fill the cells. This type of mycorrhiza resembles the ectomycorrhizas formed with forest trees but differs from them because of the cell penetration. The fungi involved are Basidiomycetes and mainly species that form ectomycorrhizas with forest trees.

The presence of the fungal sheath, as in ectomycorrhizas, insulates the host from the soil. Hence all minerals absorbed by mycorrhizal roots must pass through this sheath.