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Birch (Betula)

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Birch Genus Details

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Several native European and Asian species are found in the U.S., usually in the northern states. Birch are graceful, columnar trees that grow 60 to 100 feet tall and have simple, alternate leaves. The resinous, scaly bark is composed of papery layers with prominent, horizontal, corky spots. Flowers occur as separate pendulous staminate catkins and smaller, upright pistillate (cone-like) catkins on the same tree. Flowering occurs in early spring before or at the time leaves appear for a short period of about 7 days. All species are wind-pollinated and species flower in succession at different times, some species overlapping, so massive amounts of pollen may shed over several weeks.
Paper birch (Betula papyrifera)
Paper birch (Betula papyrifera)
River birch (Betula nigra)
River birch (Betula nigra)

Birch Allergy Info

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Birch species are reported to cause severe pollinosis where large numbers are present, and cause the same types of allergies. Pollen allergenicity has been well documented in Europe. Birches have been reported to rank second to the oaks in importance for causing pollinosis among tree types. Birch pollen allergenicity has been reported to be more frequent east of the Rocky Mountains.

Birch Pollen Description

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The grains are suboblate to oblate; the amb triangular with convex sides. The pollen has 3 strongly-aspidate pores.
Grains are 18-23 x 21-30 micrometers in size.
Birch genus, single grain
Birch genus, single grain
Birch genus, multiple grains
Birch genus, multiple grains

Species in This Genus

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Allergenicity Legend:
Mild Allergen Mild Allergen  |  Moderate Allergen Moderate Allergen  |  Severe Allergen Severe Allergen  |  Allergy Test Allergy Test Available
Birch (Betula) is a genus of the BETULACEAE family.
This genus includes the following allergenic species:

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Birch Genus Location

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The shaded areas on the map indicates where the genus has been observed in the United States. Click the map to see a full scale version of these allergy areas.
  - Native, observed in a county
  - Introduced, observed in a county
  - Rarely observed

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