There is one group of ectomycorrhizal fungi not likely to be observed regardless of how much one looks around on the forest floor. The reason for this is that their fruiting bodies actually occur underground. These subterranean (or hypogeous) fungi are poorly known in NCR parks because they are so difficult to collect, but results from studies carried out in other parts of the world indicate that they are probably not uncommon. Some small mammals (e.g., flying squirrels) are capable of locating and digging out the fruiting bodies of hypogeous fungi, which may represent an important food source during some parts of the year.