Dwarf mistletoe diversity in the Siskiyou-Klamath Mountain Region

Eleven taxa of dwarf mistletoes (Arceuthobium spp., Viscaceae) are known to occur in the Siskiyou-Klamath Mountain Region of southern Oregon and north ern California, making this the region of greatest species diversity of the se parasitic flowering plants in the United States. Two species, Arceuthobi um monticola and A. siskiyouense, are endemic to this region. This large di versity of dwarf mistletoes is probably a result of the wide variety of con iferous hosts that are available for colonization in the region. Twenty-one of the 22 taxa of Pinaceae occurring in the region are parasitized by one or more dwarf mistletoes to some extent.