Arceuthobium microcarpum, called the "western spruce dwarf mistletoe," is a parasitic plant known only from Arizona and New Mexico. It is found mostly on spruce trees (Picea spp.) but also occasionally on Rocky Mountain bristlecone pine (Pinus aristata Engelm.). The specific epithet "microcarpum" means "small fruited," in reference to the berries, which are only 3.5 mm long.