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| Betulaceae
The Betulaceae or Birch family is composed of 6 genera and somewhere between 120 and 150 species. Betulaceae , along with Balanopacea and Fagaceae , is a member of the Fagales or beech order of flowering plants. Members of the Betulaceae family include the true birches ( Betula ), alder and hazel trees. [ 1 ] Birch ( Betula verrucosa, B. alba) Birch is a tree common throught out Europe with the exception of the
Mediterranean. It is characterised by its white bark and is often used
as an ornamental tree. Birch pollen is common in Europe from around early-April,
but further north and in the mountains is present much later. Cross reactions
with all members of the Fagales order, such as the alder, hazel,
beech, oak and sweet chestnut. Also cross reacts with green (raw) apples.
[ 2 ]  Top Alder (Alnus glutinosa, A. incana, A. viridis)
Common in moist environments, for example along river banks. Typically flowers whenever temperatures rise significantly above 5° Celcius (i.e. generally the end of the year in Europe). One variety of alder, the green alder or Alnus viridis , which is found in the Alps blooms much later, generally in June. Alder, cross-reacts with hazel and birch pollen. Thus, those who are sensitive to one of these 3 pollens, will typically display allergic symptoms when either of the other 2 pollens are present. [ 2 ]
Top
Hazel (Corylus ) A shrub or small tree of the birch (Betulaceae) family, genus Corylus . Species include the American hazel ( C. americana ) and European hazels ( C. maxima and C. avellena ). The European trees produce edible nuts, known as hazelnuts or filberts. [ 1 ] The flowering season of the Corylus genus is weather dependent, usually taking place whenever the temoperature rises above 5° Celcius. Birch, alder and hazel all display strong cross-reactions , due to their similarity. [ 2 ] Top [1] The Encyclopaedia Britannica Online : http://www.britannica.com [2] European Pollen Information : http://www.ngdc.noaa.gov/paleo/epd/ [3] Martin, Paul S., and Drew, Charles M., 1970. "Additional scanning electron micrographs of southwestern pollen grains." Journal Arizona Academy of Sciences 6 ( 2 ): 140 - 16. Palynology Department, University of Arizona : http://geo.arizona.edu/palynology Top
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| http://www.hon.ch/Library/Theme/Allergy/Glossary/betula.html | Last modified: Wed Oct 20 2004 | |||
