THE SILVA OF COLORADO 



267 



Genus 7. SALIX, Willow 

 In addition to the trees here listed there are about twenty species of 

 shrubs in Colorado belonging to the genus Salix. Some of these extend 

 above timberline, forming, in places, dense thickets three or four feet 

 high. 



ia. Leaves-lanceolate, finely serrate, pointed. (2) 



lb. Leaves ovate, finely toothed or nearly entire, sometimes lance-elliptic or ob-ovate. 



IC. Leaves linear or narrowly lanceolate, silvery, at least when young. 



(3) 

 (4) 



Fig. 6. — Narrowleaf Willow (Salix exigua). X J 

 2a. Young twigs usually hairy; leaves firm. 

 2b. Young twigs smooth; leaves thin. 

 3a. Upper surface of leaves dark green; lower surface pale 

 3b. Upper surface of leaves pale; lower surface dull. 

 4a. Capsule glabrous when mature. 

 4b. Capsule densely white-silky, even when mature. 



Salix lasiandra Benth. 

 "Western Black Willow" 

 Salix amygdaloides Anders. 

 "Peach Willow" 



Salix nuttallii Sarg. 

 "NuttalPs Willow" 

 Salix bebbiana Sarg. 

 "Bebb's Willow" 



Salix exigua Nutt. 



"Narrowleaf Willow" 

 Salix sessilifolia Nutt. 

 "Narrowleaf Willow" 



Genus 8. BETULA, Birch 



In addition to the two trees of this genus there is a dwarf shrub 

 {Betula glandulosa Michx.) along streams at high altitudes. 



