Larch dwarf mistletoe Larch dwarf mistletoe

Arceuthobium douglasii Engelmann var. laricis M. E. Jones, Biol. Ser. Bull. State Univ. Montana. 15: 25. 1910; A. laricis (M. E. Jones) H. St. John; Razoumofskya laricis (M. E. Jones) Piper

Plants forming witches' brooms. Stems green, olive green, maroon, or purple, 4(–6) cm; third internode 5–8(–14) × 1–1.3(–2.5) mm, dominant shoot 1.5–3 mm diam. at base. Staminate flowers 2.7 mm diam.; petals 3(–4). Fruits 3.5 × 2.5 mm.

Flowering Jul–Aug; fruiting (Aug–)Sep(–Oct). Coniferous forests, especially with western larch or mountain hemlock; 600–2300 m; B.C.; Idaho, Mont., Oreg., Wash.

Meiosis occurs in June, with fruits maturing 13–14 months after pollination.

Larix occidentalis and Tsuga mertensiana are the principal hosts for subsp. laricis; secondary to rare hosts include Abies grandis, A. lasiocarpa, Picea engelmannii, Pinus albicaulis, P. contorta, P. monticola, and P. ponderosa. This dwarf mistletoe is a major pathogen on larch in Idaho and Montana.