|Size||11 - 25 um in diameter|
|Shape||more or less spheroidal|
|Exine||1 - 1.6 um thick|
|Pores||usually 2, but can be 3 or 4, slightly aspidate, opercula centrally thickened and often protruding|
|Bloom Period||March - May, and to June in Northern regions|
|Allergenicity||strong, capable of causing severe pollinosis|
Dr. M. Davis images:
Bassett, John, Clifford Crompton and John Parmelee. An Atlas of Airborne Pollen Grains and Common Fungus Spores of Canada. Canada Department of Agriculture, 1978.
Jelks, Mary, M.D. Allergy Plants that Cause Sneezing and Wheezing. World Wide Printing, Tampa, 1986.
Kapp, Ronald O. Pollen and Spores, Second Edition. The American Association of Stratigraphic Palynologists Foundation, 2000.
Lewis, Walter H., Prathibha Vinay and Vincent E. Zenger. Airborne and Allergenic Pollen of North America. The Johns Hopkins University Press, Baltimore and London, 1983.
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