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Birches (genus Betula) are one of the world’s most widely distributed woody plant, living across every continent in the northern hemisphere particularly in northern temperate and boreal climates near water.  The family Betulaceae, to which they belong, also contains the alders, hazels and hornbeams.  Birches are broadleaved deciduous hardwoods, typically short-lived species that often grow as small- to medium-sized tree and shrub pioneers into disturbed areas.

In response to evolutionary and recent climate change patterns, birch species have diversified morphologically, genetically, ecologically and physiologically.  Like many wind-pollinated species, much hybridization and polyploidy has occurred among birches, leading to poor consensus about individual species.  The genus is variously described as containing between 30-60 known species, broken into five groups (although other schemes have also been proposed):
   wintergreen birches (Betulenta)
   broadleaf birches (Betulaster)
   costate birches (Neurobetula)
   typical birches (Betula)
   dwarf birches (Chamaebetula)
Recent nuclear molecular phylogenetic study, however, suggests that Neurobetula and Chamaebetula may not form true (monophyletic) groups (Wikipedia 2014; Li et al. 2007)

Birches are recognizable by characteristic, conspicuous horizontal markings (lenticels) on their bark.  The bark often separates into thin, papery plates, and many species produce resinous oil making it resistant to decay.  Human cultures as early as the 1st Century CE and continuing to the current day have used bark from various birch species as paper for writing (Wikipedia 2 September 2014).  Medical properties and the nutritional value of birch bark have also been appreciated since prehistory, and for some time the cosmetic industry has exploited and explored chemicals in birch bark.  In the last decade, phytochemicals isolated from the bark of many species show great promise for multiple uses, including new drug development.  One example is recently recognized activities of birch bark triterpenoids, which represent a new class of anti-cancer and anti-HIV substances with a novel mechanism of action (Ebeling et al. 2014; Krasutsky 2007). 

Birch wood is fine grained, attractive, hard, flexible and strong and used for many building purposes as well as for quality, highly flamable firewood.  Birch sap is harvested for syrup and fermented drinks, e.g. birch beer (Wikipedia 26 September 26, 2014). 

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