24 Betulaceae. 



1. Lateral buds ellipsoid or oblong, very blunt, small. 2. 

 Buds ovoid or fusiform-oblong, acute, at most ciliate. 8. 



2. Buds very small (3 or exceptionally 4 mm.). 3. 

 Buds moderate for the group (4 mm.): bark papery. 5. 

 Buds large for the group (5 mm.): bark papery. 7. 



3. Twigs not resinous warty, softly hairy. B. pumila. 

 Twigs with resinous warts. 4. 



4. Twigs and buds with soft hairs. B. pumila glandulifera. 

 Twigs and buds only velvety. (1). B. glandulosa. 



5. Buds hairy: twigs warty: bark orange. (2). B. nigra. 

 Bud-scales at most ciliate: bark creamy or white. 6. 



6. Twigs very resinous-warty: glabrous. (3). B. populifolia. 

 Twigs sometimes with long hairs. (4). B. papyrifera. 



7. Buds glabrous: bark creamy or white. B. papyrifera. 

 Buds hairy: lower scales long: bark orange. B. nigra. 



8. Buds acutely ovoid. 9. 



Buds subfusiform, acute, with short lower scale. 12. 



9. Twigs puberulent, somewhat warty. B. kenaica. 

 Twigs glabrate. 10. 



10. Twigs resinous-warty: buds small (3X5 mm.). B. utilis. 

 Twigs little warty: buds larger (4-5X6-8 mm.). 11. 



11. Twigs and buds red-brown. (5). B. Maximowiczii. 

 Twigs and buds brown. B. grossa. 



12. Buds short for the group (5-6 mm.). 13. 



Buds long (7-8 mm.): twigs scarcely warty. 17. 



13. Twigs softly hairy. 14. 

 Twigs glabrous. 15. 



14. Pubescence persistent. (6). B. pubescens. 

 Pubescent only in sheltered places. B. papyrifera. 



15. Twigs very warty and varnished. B. occidentalis. 

 Twigs sparingly if at all resinous-warty. 16. 



16. Bark white: trees usually weeping. (7). B. pendula. 

 Bark yellowish or silvery-gray. (Yellow birch). B. lutea. 



17. Buds light brown: branches red-brown, spicy. (8). B. lenta. 

 Buds glossy red-brown. B. japonica. 



