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UNIVERSITY OF COLORADO STUDIES 



Genus 18. RHUS, Sumac 

 This genus is represented in Colorado by Rhus rydbergii, the western 

 poison ivy and Rhus trilobata,the common "skunk bush," in addition to 

 the following species. 



I a. Usually a shrub but often tree-like at canyon mouths in rich, well-watered soil. Leaves 

 compound, of numerous pointed leaflets; turning to red or crimson in autumn. 



Rhus glabra Linn. 

 "Sumac" 



Genus 19. RHAMNUS, Buckthorn 



ia. Tree of western Colorado and westward; elliptical leaves; small greenish flowers; 

 black berry-like fruits. The bark has medicinal properties. 



Rhamnus purshiana DC. 

 "Cascara sagrada" 



Fig. 25. — Cascara Sagrada) Rham- 

 nus purshiana). X$. 



Fig. 26. — Ash (Fraxinus anomala). X\. 



Genus 20. FRAXINUS, Ash 

 Related to the "white ash" and "green ash" so commonly planted 

 for shade. The Colorado species has the typical flower and fruit struc- 

 ture of the ash but the leaf is not usually compound. 



1 a. Leaf simple, or occasionally with two or three leaflets; fruit a winged samara. Occur- 

 ring in canyons of the southwestern part of the state. 



Fraxinus anomala Torr. 



