About Arceuthobium campylopodum subsp. littorum (Hawksw., Wiens & Nickrent) Nickrent
Morphology: For the first few years of its life, this mistletoe develops haustoria — a network of internal tissues that grow inside its host plant. These haustoria connect to the host’s xylem to extract water and to the host’s phloem to extract nutrients. Once this internal endophytic system is fully established, the plant grows a network of aerial shoots that break through the host tree’s bark. The aerial stems are green, brownish, or yellow, branch in a flabellate pattern, and reach approximately 10 cm in length. The stems of Arceuthobium 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 tiny scales that clasp the stems. Both stems and leaves contain chlorophyll, but they have a low photosynthetic rate, so the plant continues to rely on its host for the majority of its carbohydrates. Distribution: A. campylopodum has a broad geographic range that largely matches the range of its main 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 m. Many sources that describe a much wider geographic range for A. campylopodum, such as the Flora of North America, use a broader taxonomic definition of the species that includes most or all species within Section Campylopoda. In Oregon and Washington, the species’ range extends north to south along the east side of the Cascade Range, and also stretches through northeastern Washington and the Blue Mountains into most of western Idaho. To the south, it grows through 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 near Lake Tahoe. The southern part of the species’ distribution includes several separate population groups: across the Transverse Ranges of southern California, along the Peninsular Ranges from southern California into Baja California (including the Sierra de Juárez and Sierra de San Pedro Mártir), and in the Spring Mountains of southern Nevada. Flowers and reproduction: Arceuthobium campylopodum is dioecious, meaning each individual plant produces only male (staminate) or only female (pistillate) flowers. Male flowers have three or four petals and measure 3.1–4.2 mm in diameter. Flowering (anthesis) occurs from mid-August to late September, with peak bloom 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 5–6 mm long and 3 mm wide. It is typically 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 seed ejection, 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 makes up roughly one-third of the fruit’s total mass, and helps ejected seeds stick to the foliage or branches of any potential host tree they hit. Uses: Some Plateau Indian tribes used western dwarf mistletoe as a wash to prevent dandruff.
