BETULACEAE 25 



CARPINUS. Hornbeam. Blue Beech. 



Deciduous small trees with fluted trunks; smooth gray bark; 

 pale hard wood with minute diffused ducts and extremely fine 

 medullary rays; slender zig-zag terete twigs; rather round 

 homogeneous pale pith; alternate 2-ranked low small crescent 

 shaped leaf-scars with 3 bundle traces; narrow stipule-scars; 

 elongated ovoid rather small sessile buds with several spir- 

 ally placed smooth scales, the end bud lacking; simple doubly 

 serrate petioled moderate leaves; inconspicuous monoecious 

 apetalous flowers in small catkins; and small ribbed seed-like 

 fruits, each subtended by a hastate bract. 



1. Bracts acute, sharply serrate. C. caroliniana. 

 Bracts blunt, not serrate. (European). 2. 



2. Tree round-topped. 3. 



Tree conical. C. Betulus pyramidalis. 

 3- Leaves green. 4. 



Leaves for a time purple. C. Betulus purpurea. 



4. Leaves merely toothed. C. Betulus. 



Leaves cut or lobed. C. Betulus incisa. 



BETULA. Birch. 



Deciduous trees or occasionally shrubs often with papery- 

 flaking or white bark with transversely elongated lenticels; pale 

 or reddish often hard wood with minute diffused ducts and 

 very fine medullary rays; mos<tly very slender terete twigs; 

 small 3-sided or flattened homogeneous greenish pith; alter- 

 nate often 2-ranked low rather crescent-shaped leaf-scars with 

 3 bundle-traces; short narrow evanescent stipule scars; ovoid or 

 oblong sessile solitary buds, the terminal present on spurs and 

 the lateral rather appressed with about 6 alternate exposed 

 scales; simple usually toothed petioled leaves; small imperfect 

 inconspicuous apetalous flowers in catkins; and small 2-wing- 

 ed fruits in cone-like catkins with deciduous 3-lobed scales. 



1. Shrubs. 2. 

 Trees. 4. 



2. Leaves glabrous. 3. 



Leaves pubescent, dentate. B. pumila. 



