FLOWERING PLANTS AND FERNS OF ARIZONA 217 



petioled or sessile, with mostly lanceolate blades; stipules large or 

 small, persistent or fugacious; catkins not pendulous; stamens 2 

 to 10. 



The genus is a difficult one and the Arizona species require further 

 study. Most of the specimens in herbaria are incomplete, as leaves, 

 staminate flowers, and fruit are needed for accurate determination 

 of many of the species. The following treatment must be regarded 

 as only provisional. 



Willows grow mostly along streams and are valuable for their shade, 

 especially on the stock ranges in the southern part of the State, 

 where S. gooddingii, Arizona's largest willow, is widely distributed 

 and common. The foliage is eaten by livestock and the bark by 

 beavers. Small roots develop in abundance, and thus the willows 

 are important agents in checking soil erosion along watercourses. 

 In high mountains S. scouleriana, in particular, invades burned forest 

 areas, holding the soil and acting as a nurse for the reproduction of 

 conifers in much the same way as the aspen. The Pima and other 

 Indians of Arizona used willow twigs for basket material. Timbers 

 bound with willow withes have been found in cliff dwellings. The 

 drug salicin, obtained from the bark of various species, has tonic, 

 antiperiodic, and febrifugal properties. 



Key to the species 



1. Petioles none or very short (not more than 3 mm. long) ; leaf blades sericeous, 

 at least beneath, linear-lanceolate or narrowly oblanceolate, seldom more 

 than 7 mm. wide and usually much narrower, the margins entire or re- 

 motely denticulate; stamens 2 (2). 

 2. Leaf blades oblanceolate, sessile or very nearly so, at maturity not more than 

 3 cm. long; capsules silky-villous, then glabrate 1. S. taxifolia. 



2. Leaf blades linear-lanceolate, short-petioled, at maturity 5 cm. long or 



longer; capsules glabrous 2. S. exigua. 



1. Petioles more than 3 mm. long or, if shorter, the larger blades more than 7 mm. 

 wide, or closely serrate or serrulate (3) . 



3. Margins of the leaf blades entire or nearly so, the lower surface more or 



less glaucous (4). 

 4 . Upper surface of the mature leaves pubescent, not shiny ; leaf blades usually 

 less than 3 times as long as wide, elliptic, oblong, or oblong-lanceolate; 

 pistillate catkins seldom more than twice as long as wide at maturity; 



capsules pubescent 3. S. bebbiana. 



4. Upper surface of the mature leaves glabrous, often shiny (5). 



5. Leaf blades obovate, rounded to acutish at apex; capsules silky-villous. 



4. S. SCOULERIANA. 



5. Leaf blades lanceolate or oblanceolate, acute to acuminate at apex; 

 capsules glabrous (6) . 

 6. Shrub up to 4 meters high; branchlets usually dark purple (plum- 

 colored) and very glaucous 5. S. irrorata. 



6. Shrubs or trees ; branchlets yellowish to dark brown, not or but slightly 

 glaucous (7). 

 7. Leaf blades prevailingly oblanceolate and acute or short-acuminate ; 



stamens 2, the filaments glabrous 6. S. lasiolepis. 



7. Leaf blades prevailingly lanceolate or oblong-lanceolate and long- 

 acuminate; stamens more than 2, the filaments hairy toward 



the base 7. S. laevigata, 



3. Margins of the leaf blades closely serrate or serrulate (8). 



8. Lower surface of the leaf blades green, slightly paler than the upper surface 

 but not glaucous (9). 



9. Petioles and leaf bases glandular 8. S. caxjdata. 



9. Petioles and leaf bases not glandular; branchlets yellowish; leaf blades 

 lanceolate, often narrowly so, long-acuminate at apex, attenuate at 

 base 9. S. gooddingii. 



