242 American Midland Naturalist Monograph No. 4 



3. Dwarf Rabbitbrush {Chrysothamnus depressus Nutt.). — Dwarf 

 shrub, 1/3 to 1 foot high, usually with whitish branches and leaves; leaves 

 short, thickish, narrowly oblong to lance-shaped, 1/6 to % inch long, rather 

 sharp-pointed; flowering heads about % inch high, few-flowered (about 5 in a 

 head), borne in flat or round-topped clusters; bracts of involucre boat-shaped, 

 short-pointed, arranged in 5 sharply defined vertical rows: achenes more or 

 less 4-angled, tapering to the base, smooth or obscurely hairy towards the 

 summit; occurs only in parks of the Southwest. This species is often closely 

 browsed, but it is not usually found in great abundance. 



Occurrence. — MESA verde : head of old Switchback road, 8,100 feel. GRAND CAN- 

 YON. South Rim, about 7,000 to 7,500 feet: 2 miles south of Moran Point; Grand 

 X'lew. Canyon: Bright Angel trail. 



4. Southwest Rabbitbrush (Chrysothamnus pnlchellus (Gray) 

 Greene) . — Similar in appearance to dwarf rabbitbrush; differs in having nar- 

 rower filiform leaves and in having somewhat larger flowers (about i/4 inch 

 high) ; the heads in fruit appearing as tiny brooms because of the long, 

 straw-colored pappus bristles (sometimes nearly i/^ inch long) . 



Occurrence. — ZION. 



5. Douglas Rabbitbrush (Chrysothamnus vlscidiflorus (Hook.) 

 Nutt.). — A very variable species with many varieties; shrub 1^/2 to 4 feet 

 high, the stems white or pale green; leaves narrowly linear to oblong-lance- 

 shaped, % to 2^4 inches long, 1- to 3-nerved (or 5-nerved in variety), often 

 twisted, smooth but sticky; flower heads borne in broad spreading, oblong to 

 rounded or flat-topped clusters, the flowering branches rather glutinous; in- 

 volucre about y^ inch high, the bracts oblong to linear, boat-shaped, not ridged 

 on the back, arranged in poorly defined vertical rows; flowers about 5 to a 

 head; seed-like achenes usually densely hairy. A chewing gum made from the 

 roots of this plant was used by the Indians of certain regions of the Southwest. 



Field Guide to the Varieties 



Leaves somewhat glandular or sticky-glutinous, not hairy or hairy only on the mar- 

 gins; branches of flower clusters not hairy. 

 Leaves dark green, 4/5 to 2 inches long, linear or linear-lance-shaped. 



Plants mostly more than V/j feet high 5. C. viscidiftorus. 



Plants less than l'/2 feet high 5a. Var. pjmilus. 



Leaves pale green, narrowly linear-filiform, % to 1-1/5 inches long, the mar- 

 gins usually inrolled 5b. Var. slenophpllus. 



Leaves, at least the upper, more or less hairy; branches of flower-clusters hairy. 



Leaves densely rough-hairy, usually not twisted; bracts of involucre not thick- 

 ened at tips 5c. Var. lanceolalus. 



Leaves finely hairy, usually twisted; bracts of involucre with a somewhat thick- 

 ened spot at tips 5d. Var. elegans. 



Occurrence (C. viscidiftorus). — LASSEN. YOSEMITE: east of Yosemite Valley. YEL- 

 LOWSTONE: north of Mammoth auto camp. GRAND TETON. ROCKY MOUNTAIN, rare: 

 near Eagle Cliff; Estes Park, 7,500 feet. BRYCE CANYON. 



5a. Mountain Rabbitbrush (Var. pumilus (Nutt.) Jepson). — Low 



