Bristlecone pine dwarf mistletoe: Arceuthobium microcarpum subsr aristatae (Viscaceae), a new subspecies of western spruce dwarf mistletoe from northern Arizona

We describe Arccuthobium microcarpum subsp. aristatae (Viscaceae), a parasite of bristlecone pine (Pinus aristata Engelm.) and Engelmann spruce (Picea engelmarmii Parry ex Engelm.) in northern Arizona. Morphological and phenological data were used to compare A. microcarpum populations parasitizing bristlecone pine on the San Francisco Peaks, Arizona, with populations on Engelmann spruce and blue spruce (Picea pungens Engelm.) from other locations in Arizona and New Mexico. Morphological, phenological, and host susceptibility differences support the classification of the populations of A. microcarpum on the San Francisco Peaks and Kendrick Peak in northern Arizona as a new subspecies.