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Alder (Alnus)

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Alder Genus Details

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Alders are deciduous trees or large shrubs that often grow together in moist soils in wooded areas of North America. All species have separate drooping male and upright female flowers on catkins of the same plant. Flowering precedes the opening of leaf buds and usually occurs during January to April depending on latitude and elevation.
European Alder (Alnus glutinosa).
European Alder (Alnus glutinosa).
Speckled Alder (Alnus incana).
Speckled Alder (Alnus incana).

Alder Allergy Info

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All species have windborne pollen which has been reported to be a significant allergenic cause. People sensitive to one alder species are usually sensitive to all species.

Alder Pollen Description

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Pollen grains of Alnus are oblate to oblate-spheroidal and usually 4-5 porate. Their exinous thickened bands that extend in pairs from aperture to aperture distinguish the grains.
Pollen grains vary in size from 19-21 x 23-30 micrometers.
Alnus rugosa, single grain
Alnus rugosa, single grain
Alnus rugosa, multiple grains
Alnus rugosa, 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
Alder (Alnus) is a genus of the BETULACEAE family.
This genus includes the following allergenic species:

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Alder 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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