Triploidy is a form of polyploidy – specifically, the condition of having three copies of the genome in each cell. Triploid plants are expected to have low fertility, and may show growth or metabolic characteristics which differ from diploid forms. In aspen, we have discovered that aspen populations in western North America contain a high proportion of triploids, and that the occurrence of triploids corresponds roughly with climate variables. Further, we find that the largest aspen clones tend to be triploid. Taken together, these findings suggest that triploid clones have enjoyed a vegetative advantage over diploids in western landscapes. We discuss the methods for detecting triploidy, potential environmental susceptibilities of triploids, and management strategies favoring diploid vs. triploid aspen.