THE BIRCH FAMILY 



BETULACE.E Agardh 



'^b'- 



IX genera compose this family, including about 80 species of trees and 

 shrubs, mostly indigenous to the cooler portions of the northern 

 hemisphere, where they are of considerable economic importance. 

 The wood of several species of Alders is highly prized by gunpowder 

 manufacturers, as the source of very superior charcoal; their bark is also valued 

 in tarming and to some extent as an astringent medicine. The fruits of most of 

 the species of Corylus, variously known as Filberts or Hazelnuts, are important as 

 food. Some of the Birches, especially Betula lenta yield an aromatic volatile 

 oil of importance in medicine and as a flavoring agent. The bark of Betula 

 papyrijera was of considerable importance in former times as a material for 

 canoe-building. 



' The Betulaceae have alternate deciduous simple leaves, with usually decid- 

 uous stipules. The small flowers are monoecious; the staminate in long, usually 

 drooping catkins, solitary or in clusters of 2 or more, in the axils of numerous 

 bracts, with or without a perianth, stamens 2 to 10, their filaments separate, anthers 

 2-celled, the sacs sometimes distinct on a 2-forked filament. The pistillate inflo- 

 rescence is of spike-like or capitate catkins, the flowers with or without a perianth; 

 perianth, if present, adnate to the i- or 2-celled ovary; style 2-cleft or divided; 

 ovules I or 2 in each cell, pendulous. The fruits are mostly small, i -celled, 

 i-seeded nuts or samaras, subtended by usually enlarged bracts, forming a 

 cone-Uke structure called a strobile; seed coat membranous; endosperm none; 

 cotyledons fleshy. 

 Our genera are: 



Staminate flowers solitary in the axil of each bract, without a perianth; pistillate 

 flowers with a perianth. 

 Staminate flowers without bractlets; pistillate flowers numerous, spicate; nut 

 small, subtended by a large bract. 

 Fruit-bracts flat, leaf-like, 3-lobed. i. Carpinus. 



Fruit-bracts closed, membranous. 2. Ostrya. 



Staminate flowers with bractlets; pistillate flowers few, in heads; nut large, in 



a leaf-like involucre. 3. Corylus. 



Staminate flowers 2 or more in the axil of each bract, with a perianth; pistillate 

 flowers without a perianth. 

 Stamens 2; bracts of the ripe fruit membranous and deciduous with the 



nut. 4. Betula. 



Stamens 4, sometimes 3 to 6; bracts of the ripe fruit woody and persistent after 



the nut has fallen out. 5. Alnus. 



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