The classification of the dwarf mistletoes comprising the Arceuthobium campylopodum-occidentale complex continues to be one of the most difficult taxonomic problems associated with this important group of parasitic flowering plants. The complex consists of four taxa: A. campylopodum Engelmann, A. occidentale Engelmann, A. littorum Hawksworth, Wiens & Nickrent, and A. siskiyouense Hawksworth, Wiens & Nickrent; all of which are morphologically similar, flower and disperse seed in the fall, and parasitize hard pines. We collected morphological measurements for these four taxa from throughout their geographic ranges and used non-parametric and multivariate statistical analyses to compare morphological differences among them. Our analyses demonstrated that male plants of A. littorum and A. siskiyouense can be delimited morphologically; therefore, we recommend that both taxa continue to be recognized as species. Although, our results indicated that A. occidentale is very similar morphologically to A. campylopodum, it can be distinguished from the latter species using morphological characters, particularly for female plants. Furthermore, because A. occidentale flowers and disperses seed nearly one month later than A. campylopodum, we recommend it continue to be treated at the species level pending additional study. Comparative morphological and phenological differences between and among the species studied herein are summarized and can be used for field/laboratory diagnosis of these taxa.