About Arceuthobium campylopodum subsp. tsugense (Rosend.) Nickrent
The accepted scientific name of this subspecies is Arceuthobium campylopodum subsp. tsugense (Rosend.) Nickrent. For the first several years of its life, this mistletoe develops an internal tissue system called haustoria inside its host plant. Haustoria connect to the host’s xylem to take water, and to the host’s phloem to take nutrients. Once this internal endophytic system is fully established, the plant grows a network of aerial shoots that push out through the host tree’s bark. These aerial stems are colored green, brownish, or yellow, branch in a flabellate pattern, and reach approximately 10 cm in length. The stems of Arceuthobium campylopodum are often thicker and more robust than stems of two sympatric closely related species: A. siskiyouense and A. occidentale. Its leaves are very small, reduced to scale-like structures that clasp around the stems. Both stems and leaves contain chlorophyll, but their photosynthetic rate is low, so the plant still relies on its host for most of its carbohydrates. Arceuthobium campylopodum has a wide geographic distribution that largely overlaps with the range of its primary host, Pinus ponderosa. It occurs across much of the western United States including Washington, Oregon, Idaho, California, and Nevada, as well as Baja California. It grows at elevations between 30 and 2500 m. Many sources that report a much larger range for this species, such as the Flora of North America, use a broader taxonomic definition that includes all or nearly all species in Section Campylopoda. In Oregon and Washington, the species’ range runs north-south along the eastern side of the Cascade Range. It also extends through northeastern Washington and the Blue Mountains into most of western Idaho. To the south, it grows in the Klamath-Siskiyou region of southwestern Oregon and northwestern California. Its range continues south through California along the Northern Coast Range and the Sierra Nevada, reaching into Nevada around Lake Tahoe. The southern end of the species’ distribution includes several separate population groups: populations in the Transverse Ranges of southern California; populations along the Peninsular Ranges from southern California into Baja California, including the Sierra de Juárez and Sierra de San Pedro Mártir; and populations in the Spring Mountains of southern Nevada. Arceuthobium campylopodum is dioecious: each individual plant produces only male (staminate) or only female (pistillate) flowers. Male flowers have three or four petals, and measure 3.1 to 4.2 mm in diameter. Flowering (anthesis) occurs from mid-August to late September, with peak blooming from late August to mid-September. This flowering time is earlier than that of the closely related A. occidentale, and later than that of A. siskiyouense. The fruit is an oblong berry that averages 5 to 6 mm long and 3 mm wide. It is typically light green, but may look bluish gray or glaucous due to a waxy surface coating. All mistletoes growing on a single host tree can collectively produce between 800 and 2.2 million seeds each year. Peak seed dispersal happens from mid-September to mid-October. Hydrostatic pressure building inside the fruit causes explosive ejection of the seed, with an initial velocity of approximately 27 m/s (89 ft/s) and an average dispersal distance of 10.7 m. A sticky substance called viscin forms around one-third of the fruit’s total mass, and helps the seed adhere to the foliage or branches of any potential host tree it contacts. Some Plateau Indian tribes used western dwarf mistletoe as a wash to prevent dandruff.
