Ectomycorrhizae.
The fungal mycelium (mass of branching hyphae) forms a sheath ("mantle") over the surface of the root.

The hyphae extend into the soil, absorbing water and minerals.

Hyphae also extend into the extracellular spaces of the root cortex, forming a "Hartig net", providing extensive surface area for nutrient exchange between the fungus and its host plant.