10 Salicaceae. 



1. Weeping. P. Tremula pendula. 

 Fastigiate. 2. 



Neither weeping nor fastigiate. 3. 



2. Twigs and plump buds woolly. 



(Bolles' poplar). P. alba Bolleana. 

 Twigs and slender buds glabrous. 



(Lombardy poplar). P. nigra italica. 



3. Lateral buds plump, with 4 or more exposed scales. 4. 

 Lateral buds often elongated, mostly with 3 exposed 



scales. (Cottonwoods and Balsams). 8. 



4. Buds glabrous or glabrate. 5. 



Buds persistently silky or tomentose. 6. 



5. Buds glabrous, somewhat gummy. 



(American aspen). (1). P. tremuloides. 

 Buds somewhat downy. (European aspen). P. Tremula. 



6. Twigs glabrous. (Large-toothed aspen). P.grandidentata. 

 Twigs tomentose. 7. 



7. Tomentum gray. (Gray poplar). P. canescens. 

 Tomentum white. (Silver poplar). P. alba. 



8. Buds short and broad, dark and brown. 



(Swamp Cottonwood). (2). P. heterophylla. 

 Buds elongated, often gummy. 9. 



9. Twigs green or gray or buff, glabrous. (Cottonwoods). 10. 

 Twigs brown or red-brown, somewhat villous. 



(Balm-of-Gilead). (3). P. candicans. 



10. Trees oblong, with ascending branches. 



("Carolina cottonwood"). X P. Eugenei. 

 Tree ovoid or open. 11. 



11. Of moderate growth: twigs rather slender. 



(European black poplar). P. nigra. 

 Large: twigs rather stout: native. 12. 



12. Buds glabrous. (Common eastern cottonwood). 



(4). P. deltoides monilifera. 

 Buds minutely velvety: Western. 



(Plains cottonwood). P. Sargentii. 



