240 American Midland Naturalist Monograph No. 4 



tony or nearly smooth; flowers yellow, covering the bushes with golden color 

 during the summer; flower heads borne in dense, spreading, usually flat- 

 topped or rounded clusters; bracts of involucre arranged in distinct vertical 

 rows. 



The common name comes from the fact that the plants have a high 

 rubber content. They have been shown to contain a fairly high grade of 

 rubber which vulcanizes easily. The species occurs commonly on alkaline 

 soil. The herbage is not ordinarily palatable to animals, probably because 

 of the disagreeable rubbery taste. The Indians of certain areas used the 

 plant to make a crude chewing gum. 



Field Guide to the Varieties 



Twigs usually densely leafy; flower clusters flat-topped, rounded, or elongated; 

 achenes densely hairy. 



Bracts of involucre gradually pointed or blunt, not abruptly pointed. 



Involucres somewhat hairy or fuzzy (at least the shorter outer bracts) ; 

 plants about 2/3 to 2 feet high, usually rounded. 



Involucres mostly '/4 to 1/3 inch high, the bracts blunt, not strongly 



ridged en the back; plants woody only at base 



2. C. nauseosus. 



Involucres mostly 1/3 to 2/3 inch high, the bracts pointed, strongly 



ridged on the back; plants distinctly shrubby 



2a. Var. speciosus. 



Involucres smooth, the bracts pointed, ridged on the back; shrubs commonly 

 2 to 5 feet high, taller than broad. 



Flower clusters rounded or flat-topped 2b. Var. graveolens. 



Flower clusters elongated or cylindric 2c. Var. cojisimilis. 



Bracts of involucre abruptly pomted; occurs only in California parks 



2d. Var. occidentalis. 



Twigs rush-like, leafless or very sparsely leafy; flower clusters flat-topped; achenes 

 hairy or smooth; species of the Southwest. 



Shrubs 2 to 3 feet high; bracts of involucre pointed, smooth; achenes densely 



hairy 2e. Var. jiinceus. 



Shrubs about 1 foot high; bracts of involucre blunt, margins hairy, the backs 



fuzzy; achenes smooth 2f. Var. glareosus. 



Occurrence (C. nauseosus). — Yellowstone, rare: Gardiner; Mammoth Hot 

 Springs; Tower Falls. GRAND TETON. GRAND CANYON. South Rim. Canyon: Bright 

 Angel trail along Garden Creek; Kaibab trail about 1 mile below South Rim; Bright 

 Angel Creek several miles above Phantom Ranch. 



2a. Tall Rabbitbrush (Var. speciosus (Nutt.) Hall). — Shrubs mostly 



about I1/2 feet high; leaves 2/3 to 2 1/3 inches long, up to ^ inch wide, 1- 



nerved; heads borne in more or less rounded or somewhat elongated spreading 



clusters at the ends of the branches; involucres 1/3 to 2/5 inch high, the bracts 



pointed, strongly ridged down the backs; seed-like achenes densely hairy. 



Occurrence. — CRATER LAKE: Pumice Point; around the lake at about 8,250 feet. 

 YOSEMITE, 4,000 to 9,000 feet: south of Mather (near park); Mono Pass. YELLOW- 

 STONE. 



2b. Greenplume Rabbitbrush (Var. graveolens (Nutt.) Piper). — 



