12 General Key to the Families 



4. S. Bebbiana. Sargent. Brown Willow. 



5. S. nivalis. Hook. Alpine Willow. 



6. S. petrophila. Rydb. Dwarf Willow. 



7. S. vestita. Pursh. Hairy Willow. 



8. S. sitchensis. Sanson. Sitka Willow. 



9. S. arctica. Pall. Arctic Willow. 

 II. POPULUS. (Tourn.) L. 



1. P. tremuloides. Michx. Aspen Poplar. 



2. P. balsamifera. L. Balm of Gilead. 



3. P. trichoearpa. Hook. Western Balsam Poplar. 



4. P. acuminata. Rydb. Cottonwood. 



ORDER XII. FAGALES 

 XX. BETULACE^:. BIRCH FAMILY 



Trees or shrubs ; leaves alternate, simple, straight-veined ; flowers 

 small, appearing with or before the leaves, the sterile in catkins, 

 the fertile clustered, spiked, or in scaly catkins; fruit a nut len- 

 ticular, surrounded by a wing. 



I. BETULA. (Tourn.) L. 



1. B. fontinalis. Sarg. Black Birch. 



2. B. alba. (L.) var. papyrifera. (Marsh.) Spach. 



Paper Birch. 



3. B. glandulosa. Michx. Dwarf Birch. 

 II. ALNUS. (Tourn.) Hill. 



1. A. sinuata. (Regel.) Rydb. Mountain Alder. 



2. A. sitchensis. Nutt. Speckled Alder. 



ORDER XIII. URTICALES 

 XXI. URTICACE^:. NETTLE FAMILY 



Herbs rarely shrubs, with watery juice, belonging to a large 

 family; leaves alternate or opposite, frequently stipulate, simple; 

 flowers a small, dioecious, moncecius or polygamous, variously clus- 

 tered; fruit an achene. 



I. URTICA. (Tourn.) L. 



i. U. Lyallii. Wats. Common Nettle. 



