I dug my fingers under it and did not feel the bulb extending below what is seen in the photos. The bulb does show a little damage though, so who knows…
A while back, a friend and I were discussing the difficulty mycologists have conducting mating studies on mychorrizal mushrooms, due to an innabilty to germinate the spores. He suggested that maybe all or most of the spores are sterile, a fluke of evolution, and that these fungi reproduce solely by cloning themselves. If this hypothesis is correct, then, as functionally a-sexual organisms, each colony would be on its own divergent evolutionary path. The energy wasted on producing mushrooms and sterile spores is enormous, but evolution is frequently not driven by efficiency; consider the peacock’s tail.
Whatever is going on, there seems to be a gradient of forms between the named species, such that one morphological species appears to bleed into another. This makes it very difficult to establish necessary and sufficient conditions for inclusion in a specific category.