Bailey & Bailey: Woody Plants of National Parks 235 



herbage dark green; leaves linear, about 1/2 to U^ inches long, smooth; 

 flower heads borne singly, about y^ to 1/2 inch high, the flowers few, yellow; 

 petal-like ray flowers none; bracts of involucre few, borne in one series, oblong, 

 dotted with dark-colored oblong oil glands; seed-like achenes linear; pappus 

 composed of rough hair-like bristles. 



Occurrence. — grand canyon, common in the canyon, 3,000 to 4,000 feet: Kaibab 

 trail below the Tonto; Bright Angel trail along Pipe Creek; Kaibab trail along Bright 

 Angel Creek. 



HoRSEBRUSH (Tetradymia DC.) 



Field Guide to the Species 



Plants not spiny; flower heads borne in more or less flat-topped clusters at the ends 



of the stems; seed-like truits (achenes) smooth or thinly hairy 



1. T. canescens var. mermis. 



Plants spiny; flower heads borne along the stems in the leaf -axils. 



Stems densely white-felty; seed-like achenes densely soft white-hairy, the hairs 

 nearly as long as the tufts of white pappus bristles, the heads thus 

 appearing as soft cotton)' balls 2. / . spinosa. 



Stems white cottony or woolly; seed-like achenes densely hairy, but the hairs 



much shorter than the tuft of pappus bristles 3. T. axillaris. 



1. Spineless Gray Horsebrush (Tecradymia canescens DC. var. in- 

 ermis Gray). — Densely branched shrub 1/3 to 2 feet high with white felty 

 herbage; leaves about ^4 to 1/2 inch long, linear or with broader tips, densely 

 white-felty, bunched at the stem joints; flowers yellow, about 4 to a head, 

 surrounded by 4 or 5 involucral bracts; heads about 1/2 inch high, borne in 

 compact more or less flat-topped clusters at the ends of the stems; seed-like 

 fruits (achenes) smooth or thinly hairy, each with a tuft of grayish bristles 

 (pappus) at the tip. It is reported that the Hopi Indians use the stems 

 and roots as a tonic. 



OccuTTence. — YELLOWSTONE, mesa VERDE. BRYCE CANYON, commcn along the rim: 

 Sunset Point; near Inspiration Point. ZION. 



2. Cotton Thorn (Tecradymia spinosa H. & A.). — Rigidly branched 

 spiny shrub, about 2 to 4 feet high, with white-felty stems; spines straight or 

 curved, I/4 to I1/2 inches long, rather crowded along the stems; leaves linear, 

 broadening slightly at the tips, bunched in the axils of the spines; flowers 

 yellow, usually 6 to 7 in a head surrounded by 5 or 6 involucral bracts, the 

 heads borne on short stems in the axils of the leaves, appearing as small cot- 

 tony balls because of the long, soft, white hairs on the seed-like achenes. 



Occurrence. — ZION : near western park boundary on road to Petrified Forest. 



3. Longspine Horsebrush (Tetradymia axillaris Nels.). — Spiny shrub 

 up to about 21/4 or 3 feet high; stems white-fuzzy or finely woolly but not cov- 

 ered with a dense felt, the upper tending to be bunched and broom-like; spines 

 straight, rigid, % to 1% inches long, at first somewhat white-woolly; leaves 

 linear, ^ to 1/2 inch long, green, somewhat fleshy, bunched in the axils of the 



