Figure 7>Z. — Wyoming big 

 sagebrush (A. tridentata 

 ssp. wyomingensisj 

 growing near Daniel ^ 

 Sublette Co., Wyoming. 



matures from September through October. In the Intermountain West, mountain big sage- 

 brush occurs in the upper elevational range of the big sagebrush zone in deep, well- 

 drained soils on mountain slopes from below 1,400 meters (4,600 feet) for f. xerioensis 

 and at elevations over 3,000 meters (9,800 feet) for f. spiciformis (Beetle and Young 

 1965; Winward 1970). The form xerioensis is unevenly topped and grows in relatively 

 dry sites similar to basin and Wyoming big sagebrush. In Idaho, this form is known to 

 occur between 780 to 1,400 meters (2,600 to 4,600 feet). Chromatographically, cytolo- 

 gically, and phenologically, xerioensis most closely resembles and is considered to be 

 a form of ssp. vaseyana (Winward 1970; Hanks and others 1973; Winward and Tisdale 1977). 

 The form epithet "xerioensis'^ has not been validly published. Winward (1970) used the 

 term. Later, he and Tisdale (1977) merely called this "X big sagebrush." Hanks and 

 others (1973) used an analogous term, low elevation vaseyana. Form spioiformis has 

 larger flower heads and leaves than typical vaseyana and is found at higher elevations, 

 usually over 2,130 meters (7,000 feet) in the cooler, more mesic sites. Vaseyana 

 grows in slightly acid to slightly alkaline soils (Welch and McArthur, data on file at 

 Shrub Sciences Laboratory, Provo, Utah). Unlike ssp. tridentata, vaseyana is rarely 

 associated with any of the saltbushes. 



Artemisia tridentata ssp. wyomingensis (Wyoming big sagebrush) is somewhat inter- 

 mediate in distribution, ecology, and morphology between basin big sagebrush and moun- 

 tain big sagebrush. Occasionally, all three subspecies may be found growing together. 

 VVhenever it is found associated with ssp. tridentata, ssp. wyomingensis is growing in 

 the poorer, more shallow soils (Beetle and Young 1965). Subspecies wyomingensis is a 

 low shrub usually less than 1 meter in height. It has an uneven top with flower stalks 

 arising throughout the crown like ssp. tridentata (fig. 33). Its main stems branch at 

 or near the ground level like ssp. vaseyana , but it does not layer. Leaves are 1 to 2 

 cm long, narrowly cuneate to cuneate (fig. 22d) , and have an average length-to-width 

 ratio of about 3:1 for the persistent leaves (Winward 1970). Flower heads contain 3 

 to 8 disc flowers and are arranged into panicles narrower than the paniculate inflores- 

 cence of tridentata and wider than the spicate inflorescence of vaseyana (Beetle and 

 Young 1965; Winward and Tisdale 1977). Flowering and seed ripening take place later 

 than vaseyana and earlier than tridentata. This subspecies may have arisen from hybrid- 

 ization between ssp. tridentata and vaseyana (Hanks and others 1973) or ss'p . tridentata 

 and A. nova (Winward 1975) . Wyoming big sagebrush grows throughout the Intermountain 

 region (fig. 34) . It is particularly abundant east of the Continental Divide in 

 Montana, Wyoming, and parts of Colorado in dry, shallow, gravelly soil, usually from 

 1,500 to 2,100 meters (5,000 to 7,000 feet) (Beetle and Young 1965). In Idaho, this 

 subspecies is found from 760 to 1,980 meters (2,500 to 6,500 feet) in the hotter, drier 

 portions of the State (Winward 1970) . 



33 



