Figure 30. — Two even-aged plants 

 representing eaotypes of basin 

 big sagebrush (A. tridentata 

 ssp. tridentataj growing at 

 the Snow Field Station. The 

 form on the left was trans- 

 planted from Paradise Valley, 

 Humboldt Co., Nevada; the one 

 on the right was transplanted 

 from the Jackson Mountains, 

 Humboldt Co., Nevada. The 

 ruler in the center foreground 

 is 30 am long. 



panicles. The heads contain 3 to 6 small yellowish or brownish, trumpet -shaped, 

 perfect-disc flowers. The narrowly campanulate involucre consists of canescent bracts 

 3 to 4 mm long and about 2 mm wide that form 4 to 5 overlapping series around each head. 

 The outermost bracts are less than a fourth as long as the innermost bracts. Flowering 

 occurs from late August to October. Seed matures depending on site from October to 

 November. Basin big sagebrush is probably the most abundant shrub in western North 

 America on lowland ranges. It normally occurs on dry, deep, well-drained soils on 

 plains, valleys, and foothills below 2,130 meters (7,000 feet) elevation. Above this 

 elevation, subspecies vaseyana and occasionally subspecies wyomingensis are more preva- 

 lent. Vigorously growing basin big sagebrush is considered indicative of productive 

 ranges because it often grows in deep, fertile soil. This subspecies has generally been 

 regarded as intolerant of alkali, but there are ecotypes that grow in relatively high 

 alkalinity in association with such alkali-tolerant plants as black greasewood, shad- 

 scale saltbush, and saltgrass (Distichlis stricta) . Plants with strikingly reflexed 

 drooping branches of inflorescence are found throughout the range of subspecies triden- 

 tata. These have been termed A. tridentata ssp. tridentata f. parishii (Beetle 1959). 

 This form may be environmentally induced because some ssp. vaseyana populations of 

 central Nevada also have drooping inflorescences in some years (E. F. Schlatterer, 

 letter 12/1/77). 



Artemisia tridentata ssp. vaseyana (mountain big sagebrush) is normally a smaller 

 shrub than basin big sagebrush. Its main stem is usually divided at or near the ground, 

 and it tends to have a spreading, evenly topped crown (fig. 31). The vegetative 

 branches are usually less than 1 meter high and frequently layer at their bases. There 

 are, however, ecotypes at lower elevations that may reach about 2 meters in height. 

 The persistent vegetative leaves are broadly cuneate to spatulate and are characteris- 

 tically wider than those of both basin and Wyoming big sagebrush (fig. 22c) . When 

 looking down at this shrub, the terminal leaves on each twig appear to be distinctly 

 whorled (fig. 32). Subspecies tridentata does not show this trait. However, ssp. 

 wyomingensis shows the trait to some extent. Normally, the leaves are 2 cm long, 5 mm 

 broad, but in form spiaiformis may reach 6.5 cm long and 2 cm broad. Leaf length-to- 

 width rates for typical persistent vaseyana leaves average 4.0 while that of form 

 spiciformis averages 3.5 (Winward 1970). Crushed leaves emit a rather pleasant mintlike 

 fragrance in contrast to the more pungent odor of both basin and Wyoming big sagebrush. 

 Flower heads are arranged into narrow, often dense panicles or spikes. The heads con- 

 tain 5 to 8 trumpet -shaped, perfect-disc flowers. The broadly campanulate involucre 

 consists of numerous canescent overlapping bracts, 5 mm long and 3 to 4 mm wide. The 

 outermost bracts are less than half as long as the innermost. Some strains of mountain 

 big sagebrush start blooming as early as July and thus may be in bloom up to 6 weeks 

 earlier than either basin or Wyoming big sagebrush (Hanks and others 1973) . Seed 



31 



