 Suillus americanus is a mycorrhizal species , a mutualistic relationship where the fungus forms a sheath on the surface of the root from which hyphae extend outward into the soil , and inwards between the cortical cells with which they interface to form a Hartig net . The main benefit for the fungus is constant access to a supply of carbohydrates produced by the plant 's photosynthesis , while the plant benefits from an enhanced supply of mineral nutrients from the soil , taken up by the hyphae of the fungus . It grows in association with pines , particularly eastern white pine ( Pinus strobus ) . 
