As sclerotia are regarded all roundish or ellipsoid or oval, or irregularly shaped bodies. Mostly they have thickened and coloured walls at the outer cells, but this is not preconditional. Often sclerotia have just the same light colours as rhizomorphs or mycorrhizal mantles.
Sometimes it can be difficult to decide whether a sclerotium laying on the mantle or on rhizomorphs is definitely a sclerotium of the ectomycorrhiza in question. It has carefully to be examined for unequivocal connections between the sclerotium and those hyphae belonging without any doubt to the ectomycorrhiza forming fungus. The question is particularly difficult to handle when sclerotia are exclusively formed by emanating hyphae and just lay rather close or more remote from the ectomycorrhizae without any obvious connections. In such cases, a comparison of mantle in plan view and of the plan view of the sclerotium's outer portion can be helpful, whether identical anatomical structures can be found. In the case of Cenococcum geophilum, it could be shown that the ectomycorrhizae have the same star-like pattern (A) as the outer layers of the sclerotia (B).
 A |
 B |