a parasitic flowering plant of the genus Arceuthobium —note 1. these plants develop extensive absorption systems in the host's xylem tissue and derive most of their water and nourishment from the host; the endophytic system causes the formation of witches' brooms in some species; injury is caused by diversion of nutrients, growth reduction, and mortality —note 2. dwarf mistletoe is the most important disease problem in western coniferous forests —see leafy mistletoeThis definition last updated 10/25/2008