The nearest neighbor relations of the cryptogams growing on Quercus rubra in Michigan were investigated over whole tree trunks, and over four subsections of trunks to partially eliminate the effects of microhabitat. At all scales numerous nonrandom associations were found, indicating that it is not only gross microhabitat requirements that determine these relationships. The associations were found to differ from place to place on the tree trunk. Despite sharing the same general habitat (the tree trunk), or part of the habitat (e.g., upper north side), some species and groups of species are rarely neighbors, whereas others are far more likely to coexist and therefore interact.