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Alder Pollen

Western Red Alder Pollen

This shows two of the common forms of Western Red Alder pollen, the more common 5-pore and the 4-pore form. Crossed polarized light causes the starch grains to show as a bright speckeling inside the grain and the exine (outer wall) is birefringent (bright) in these fresh pollen grains.

Transmitted Crossed Polarized Light Illumination


Western Red Alder (Alnus rubra)

Significance in the Environment:

In the Pacific Northwest Alder pollen may appear as early as January and may persist into April. It is one of the most prolific pollen producers and will mark indoor environments with a date stamp. The fresh pollen is loaded with starch grains, which carry the allergen. The grain will be present long after the starch grains have disappeared but the allergen may still be present but now spread out onto adjacent particles as well. Check your local pollen statistics to determine the most likely time for the deposition of this pollen at your site.

Characteristic Features:

Alnus rubra has about 70% 5-pored grains, about 20% 4-pored grains, and about 10% 6-pored grains. It is stephanoporate, all of the pores are in the equitorial plane of the grain. It is strongly oblate, is granulate (scabrate), and has characteristic arcs between the pores.

Associated Particles:


Faegri, Knut and Johs Iversen, TEXTBOOK OF POLLEN ANALYSIS, Hafner Publishing Company, 1964.

Kapp, Ronald O., HOW TO KNOW POLLEN AND SPORES, Wm. C. Brown Company, 1969.

Moore, P.D., J. A. Webb, and M. E. Collinson, POLLEN ANALYSIS, Blackwell Scientific Publications, 1991

The starch bodies in the pollen grain can be seen with this type of illumination. The Starch
bodies carry the allergen in many pollens. When the grain becomes wet the starch grains are
released. The starch grains then become attached to other particles in the environment and can
be distributed in the absence of the pollen grain itself. Resuspended dusts can carry a variety
of allergens not evident by their source particles. Western Red Alder, Alnus rubra, pollen is an
oblate periporate (typically 5 pores) grain with distinctive pore structure. Alnus rubra has a
relatively high frequency of 4 and 6 pore grains as can be seen by the 4 pored grain in this image.
Alder is a prolific pollenater and in the coastal Northwest United States is frequently found in
airborne samples from early January to late February. It can often be used to indicate the presence
of dust reservoirs or time since last through cleaning in an indoor environment.