234 MISC. PUBLICATION 423, U. S. DEPT. OF AGRICULTURE 



A. vaginatum sometimes causes considerable damage in stands of 

 young yellow pine. 



Key to the species 



1. Stems slender, about 1 mm. in diameter at base, seldom more than 2 cm. 

 long, commonly scattered along the stem of the host plant, green- 

 ish 1. A. DOUGLASII. 



1. Stems relatively stout, 2 to 5 mm. in diameter at base, seldom less than 3 cm. 

 long, commonly clustered (2). 

 2. Plants yellowish, flo Bering normally in early summer; stems seldom less 



than 3 mm. in diameter at base 2. A. vaginatum. 



2. Plants olive green, brown, or sometimes yellowish, flowering in late summer; 

 stems commonly about 2 mm. in diameter at base _ 3. A. campylopodum. 



1. Arceuthobium douglasii Engelm. in Wheeler, U. S. Survey West 



100th Mer. Rpt. 6: 253. 1878. 



Razoumojskya douglasii Kuntze, Rev. Gen. PI. 2: 587. 1891 . 



Apache, Navajo, and Coconino Counties, south to Graham and 

 Pima Counties, up to 8,500 feet (perhaps higher). Western Canada to 

 New Mexico, Arizona, California, and Mexico. 



The typical form, flowering normally April to June, is parasitic on 

 Pseudotsuga. The variety abietinum Engelm. (A. campylopodum f. 

 abietinum Gill), flowering normally in August and September, 

 is parasitic on fir (Abies spp.). This variety is much less common 

 in Arizona, apparently having been collected only at the Grand 

 Canyon {Gill in 1934), and in the Pinaleno Mountains, Graham County 

 (Stouffer and Gill in 1934). 



2. Arceuthobium vaginatum (H. B. K.) Eichler in Mart., Fl. Bras. 5 2 : 



105. 1868. 



Viscum vaginatum H. B. K., Nov. Gen. et Sp. 3: 445. 1820. 

 Arceuthobium cryptopodum Engelm., Boston Jour. Nat. Hist. 

 6: 214. 1850. 



Almost throughout the State, 5,500 to 8,000 feet. Colorado and 

 Utah to western Texas, Arizona, and Mexico. 



Parasitic on pines, the presumably typical form of A. vaginatum on 

 Pinus latifalia, P. arizonica, and P. leiophylla in the south; whereas f. 

 cryptopodum (Engelm.) Gill (A. cryptopodum Engelm.), infests the 

 western yellow pine (Pinus ponderosa) in central and northern Arizona. 



3. Arceuthobium campylopodum Engelm. in A. Gray, Boston Jour. 



Nat. Hist. 6: 214. 1850. 



Razoumojskya campylopoda Kuntze, Rev. Gen. PI. 2: 587. 

 1891. 



Throughout most of the State, in various forms, 4,500 feet or higher. 

 New Mexico and Arizona to Oregon and California. 



The typical form of the species has not been reported in Arizona. 

 The f. divaricatum (Engelm.) Gill (A. divaricatum Engelm.) with the 

 old stems often conspicuously divaricate, is common in the northern 

 and central portions (Apache to Coconino and Yavapai Counties), 

 parasitic on pinyon (Pinus edulis). The f. microcarpum (Engelm.) 

 Gill (A. douglasii var.? microcarpum Engelm.) is frequent, ranging from 

 the Kaibab Plateau (Coconino County) and the White Mountains 

 (Apache County) to the Pinaleno Mountains (Graham County), 

 parasitic on spruce (Picea). The type collection of this form is from 



