Figure 6. — Low sagebrush 

 (A. arbusculaj growing 

 on the rocky flanks of 

 Indian Peak^ Beaver Co. 3 



Leaves are broadly cuneate or fan-shaped, 0.5 to 1.5 cm long, 0.3 to 1 cm wide and 

 are usually 3 (occasionally 4 to 5) toothed or cleft at the apex. Leaves on the upper 

 part of the flowering shoots may become entire. 



Flower heads are grouped into elongated, narrow racemose panicles (fig. 5a). The 

 heads usually contain from 5 to 11 disc flowers with corollas 3 to 4 mm long. The 10 

 to 15 involucral bracts are canescent. Flowering occurs from August to September, de- 

 pending upon strain and elevation. Seed ripens in October and November. Cleaned seed 

 averages 2,160 per gram (980,000 per pound) (Deitschman 1974). 



Hybridization .- -This species has a basic chromosome number of a: = 9. Both diploid 

 (2n = 18) and tetraploid (2n = 36) forms are known (Ward 1953; McArthur and Plummer 

 1978). Intermediates between low sagebrush and both A. tripartita ssp. tripartita^ and 

 A. tridentata ssp. tridentata have been reported by Beetle (1960). Hanks and others 

 (1973) found chromatographic evidence of hybridization between low sagebrush and A. 

 tridentata ssp. vaseyana. Ward (1953) united both low sagebrush and black sagebrush 

 (A. nova) into a single species partly because he felt they intergrade into one another. 



However, Ward (1953) found that most specimens of black sagebrush he examined were 

 tetraploid, whereas most specimens of low sagebrush were diploid. This difference in 

 chromosome number could be a barrier to free interbreeding, because populations of the 

 two species with the same number of chromosomes are not known to occur together. In 

 fact, the two species rarely occur together (Ward 1953). On the basis of field collec- 

 tions. Beetle (1971) argued persuasively for separate species status for the two sage- 

 brushes . 



A dwarf form of A. arbuscula occurs in the Stanley Basin area of Idaho, the 

 Jackson Hole, Wyoming area, and perhaps in other locations. Beetle (1959, 1960) named 

 this form A. arbusaula ssp. thermopo la --hot springs sagebrush. Beetle speculated that 

 this form arose as the result of hybridization between typical A. arbuscula and A. 

 tripartita. 



Distribution and habitat . --Low sagebrush grows on dry, sterile, rocky, often alka- 

 line soils betweeen 700 and 3,500 meters (2,300 and 11,500 feet) approximately 10,135,000 

 hectares (39,112 square miles) in 11 western States (Beetle 1960; Ward 1953) (fig. 6). 

 In the warmer, drier parts of its range, particularly in Nevada, it may grow well into 

 the mountains above 3,000 meters (9,800 feet). In some areas, for example, east central 

 Idaho, low sagebrush occurs on disjunct low and high elevation bands (E. F. Schlatterer, 

 letter 12/1/77). 



8 



