Arceuthobium campylopodum subsp. cyanocarpum
Plants forming witches' brooms. Stems yellow, green, olive green, or brown, 3(–7) cm; third internode 2–5.2(–14) × 1–1.1(–1.5) mm, dominant shoot 1–2 mm diam. at base. Staminate flowers 3 mm diam.; petals 3(–4). Fruits 3.5 × 2.5 mm.
Phenology: Flowering Jul–Sep; fruiting Aug–Sep.
Habitat: Coniferous forests.
Elevation: 1600–3100 m.
Calif., Colo., Idaho, Mont., Nev., Oreg., Utah, Wyo.
Meiosis occurs in July, with fruits maturing 12 months after pollination.
Subspecies cyanocarpum is widely distributed at high elevations in the western United States from the Rocky Mountains to the Sierra Nevada of California. Its most common host is Pinus flexilis; however, P. albicaulis, P. aristata, and P. longaeva are also listed as principal hosts owing to their high incidence of infection. Additional secondary to rare hosts include Picea engelmannii, Pinus balfouriana, P. contorta, P. monticola, P. ponderosa, and Tsuga mertensiana. This mistletoe is a significant pathogen in many locations, sometimes resulting in massive host tree mortality.