516 MISC. PUBLICATION 42 3, U. S. DEPT. OF AGRICULTURE 



1. Thamnosma montana Torr. and Frem. in Frem., Exped. Kocky 



Mount. Rpt. 313. 1845. 



Grand Canyon (Coconino County), Yavapai, Mohave, Pinal, 

 Maricopa, and Yuma Counties, 4,500 feet or lower, desert mesas and 

 slopes, frequent and locally abundant, February to April. Southern 

 Utah and Arizona to Sonora and Baja California. 



Turpentine-broom, so-called because of the appearance and strong 

 odor of the plant. Reported to have been used by the Indians as a 

 tonic and in treatment of gonorrhea. 



2. Thamnosma texana (A. Gray) Torr., U. S. and Mex. Bound. Bot. 



42. 1859. 



Rutosma texana A. Gray, Genera Fl. Amer. 2: 144. 1849. 

 Rutosma purpurea Woot. and Standi., Contrib. U. S. Natl. 

 Herbarium 16: 143. 1913. 



Coconino, Pinal, Cochise, Santa Cruz, and Pima Counties, 2,000 

 to 4,000 feet, dry rocky slopes and mesas, March to June. Colorado 

 and western Texas to southern Arizona and northern Mexico. 



3. PTELEA. Hoptree 



Shrubs or small trees; leaves commonly trifoliolate, the leaflets 

 lanceolate or ovate, somewhat rhombic; flowers small, perfect or 

 unisexual, in compound cymes; calyx lobes, petals, and stamens 4 or 

 5; fruit flat, nearly orbicular, winged, mostly 2-celled, indehiscent. 



The plants have a strong, somewhat disagreeable odor and are not 

 eaten by livestock. The fruits are reported to have been used as a 

 substitute for hops, in brewing. Most of the numerous forms that 

 have been described as species in this genus appear to be only individu- 

 al variations. There is great diversity in the shape and size of the 

 fruits, as well as of the leaflets, but there appears to be little correlation 

 between the characters of the 2 organs. 



Key to the species 



1. Bark of the twigs straw-colored to light olive-colored; leaves yellowish green, 

 paler but not glaucous beneath, often somewhat shiny above, rather thick 

 and firm, glabrous or sparsely pubescent beneath; leaflets prevailingly 

 rhombic-lanceolate but sometimes rhombic-ovate, the terminal one com- 

 monly 3 or more times as long as wide 1. P. pallida. 



1. Bark of the twigs brown or dark purple (commonly mahogany-colored or plum- 

 colored) ; leaves bright green or bluish green, often glaucous beneath, not 

 shiny above, thin, glabrate or permanently soft-pubescent beneath; 

 leaflets prevailingly rhombic-ovate but sometimes rhombic-lanceolate, 

 commonly less than 3 times as long as wide 2. P. angustifolia. 



1. Ptelea pallida Greene, Contrib. U. S. Natl. Herbarium 10: 70. 



1906. 



Ptelea straminea Greene, ibid. 

 ? Ptelea baldwinii Torr. and Gray, var. parmfolia A. Gray in 

 Patterson, Check List 18. 1892. 



Coconino, Mohave, and Yavapai Counties, 2,000 to 7,000 feet, 

 especially abundant in and near the Grand Canyon, May, type of 

 P. pallida from Peach Springs, Mohave County {Greene in 1889), type 

 of P. straminea from the Virgin Mountains, Mohave County (Purpus 

 6165). New Mexico and northern Arizona. 



