About Arceuthobium campylopodum A.Gray
Arceuthobium campylopodum A.Gray, commonly known as western dwarf mistletoe, spends its first few years of development growing a tissue system called haustoria inside its host plant. These haustoria connect to the host's xylem to draw water and to the host's phloem to extract nutrients. After this internal endophytic system is fully established, the plant produces a network of aerial shoots that push through the host tree's bark to grow above the surface. These aerial stems are green, brownish, or yellow, branch in a flabellate pattern, and reach roughly 10 centimeters in length. The stems of A. campylopodum are typically thicker and more robust than the stems of two closely related, sympatric species: A. siskiyouense and A. occidentale. Its leaves are very small, reduced to scale-like structures that clasp around the stems. While both stems and leaves contain chlorophyll, their rate of photosynthesis is low, so the plant continues to depend on its host for most of its carbohydrates.
A. campylopodum has a broad geographic distribution that largely matches the range of its primary host, Pinus ponderosa, across much of the western United States (including Washington, Oregon, Idaho, California, and Nevada) and Baja California. It grows at elevations between 30 and 2500 meters. Many sources that report a larger range for this species, such as the Flora of North America, use a broader species definition that includes all or nearly all species classified in Section Campylopoda. In Oregon and Washington, A. campylopodum's range extends north to south along the eastern side of the Cascade Range, and also reaches through northeastern Washington and the Blue Mountains into most of western Idaho. Further south, the species occurs across 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, extending into Nevada near Lake Tahoe. The southern part of the species' distribution includes several separate population groups: populations across 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) flowers or only female (pistillate) flowers. Male flowers have three or four petals and measure 3.1 to 4.2 millimeters in diameter. Flowering (anthesis) occurs from mid-August to late September, with peak blooming from late August to mid-September. This flowering period 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 millimeters long and 3 millimeters wide. The berry is usually light green, but sometimes appears bluish gray or glaucous due to a waxy outer coating. All mistletoe plants 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 meters. A sticky substance called viscin makes up roughly one-third of the fruit's total mass, and helps the seed stick to the foliage or branches of any potential host tree it hits.
Some Plateau Indian tribes used western dwarf mistletoe as a wash to prevent dandruff.
