Figure 60. — Gray horse- 

 brush (T. canescens) 

 growing at Wahsatah 

 Station, Summit Co., 

 Utah. 



This species begins flowering about mid-June in the northern part of its range 

 (southern British Columbia and northeastern Washington) and progresses southward to 

 San Bernardino County, California, and northern Arizona where it blooms in late July 

 or early August (Strother 1974). Cleaned seed average 305 per gram (140,000 per 



Hybridization. --Gra^Y horsebrush is a polyploid species with some aneuploidy at th 

 diploid level. Sporadically, specimens with 2n = 62 chromosomes are found in diploid 

 populations (2n = 60). Triploid (2n = 90) and tetraploid (2n = 120) numbers are also 

 known. Both diploid and triploid colonies are located throughout much of the range of 

 T. canescens (Strother 1974) . 



Suggested hybrids between T. canescens and T. glabrata have been found in 

 southern Idaho where the flowering period of these two species overlap (Strother 1974) 

 A form with shorter and broader leaves, called T. inermis , occurs in Colorado, and 

 plants intermediate between this form and the normal T. canescens are as common as the 

 extremes (Harrington 1954). 



Distribution and habitat .- -The type locality for gray horsebrush is reported to b 

 the Columbia River (Abram and Ferris 1960). It is widespread, however, throughout the 

 Great Basin and adjacent areas, on dry plains, hills, and ridges from southern British 

 Columbia, Montana, Idaho, and Washington southward to New Mexico, Arizona, and Califor 

 nia between elevations of 400 and 3,300 meters (1,300 and 10,800 feet). Throughout it 

 range it is associated with the sagebrush, pinyon- juniper, and yellow pine vegetation 

 types (Strother 1974). 



Use . --This species is generally regarded to be low in palatability to most 

 animals and may be poisonous if large quantities are consumed. Nevertheless, buds 

 and young leaves are frequently browsed during spring and fall months by sheep, goats, 

 antelope, and deer. Cattle graze T. canescens fairly heavily in some areas in Nevada. 

 This shrub probably has merit for establishing cover on severely depleted soils, such 

 as mine spoils. 



Little-leaf horsebrush is a compact, heavily branched shrub up to 12 dm high. 



The vestiture of its young stems resembles that of gray horsebrush by having glabrous 



to slightly floccose streaks along the internodes below the primary leaves. These 

 streaks interrupt the otherwise feltlike tomentum. 



pound) . 



TeUadymia glabrata Torr. & Gray (littleleaf horsebrush) 



60 



