Arceuthobium microcarpum is a species of flowering plant in the family Santalaceae endemic to the coniferous forests of Arizona and New Mexico. As with other species of dwarf mistletoe, A. microcarpum parasitizes several species of conifers, relying on the host plant for water and nutrients. There are two subspecies: A. microcarpum subsp. microcarpum, commonly known as western spruce dwarf mistletoe, which parasitizes spruce trees, and A. microcarpum subsp. aristatae, commonly known as bristlecone pine dwarf mistletoe, which parasitizes bristlecone pine trees. Because of its extremely limited range, A. microcarpum is considered an imperiled species.

A. microcarpum significantly impacts the ecology of the coniferous forests, including by reducing the vitality, reproductive rate, and lifespan of host trees. They induce the formation of abnormal growths called witch's brooms in their host trees, which serve as microhabitats for wildlife. A. microcarpum also serves as a food source for birds and mammals and is itself parasitized two species of fungus.

Since its discovery in 1873, taxonomists have placed A. microcarpum under several names, and its taxonomy remains controversial. Some authorities, including the Flora of North America, treat this taxon as a subspecies of a more broadly-circumscribed Arceuthobium campylopodum, while others, including Plants of the World Online, recognize it as a distinct species.

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