Arceuthobium rubrum (Viscaceae) is a distinctive species of dwarf mistletoe having red to reddish-brown plants and red, shiny fruits. It is primarily distributed in the Sierra Madre Occidental of Durango, Mexico, but in 1972 a population of A. rubrum was reported from Oaxaca, Mexico, more than 1000 km south of the nearest population in southern Durango. Initially, this population was classified as a disjunct population of A. rubrum, but in 1989 it was described as a new species: A. oaxacanum. However, our morphological measurements and observations of the phenology for plants from Durango and Oaxaca indicate these populations are morphologically similar and flower and disperse seed at approximately the same time, supporting the results of recent molecular analyses indicating that the Oaxacan populations represent disjunct populations of A. rubrum.