Information about Corylus pollen allergenicity is limited. Pollen allergenicity has been reported in OR and MN, especially when people live near nut orchards. Hazel pollen has been reported to cross-react with birch, alder, hornbeam, and hop-hornbeam pollens.
These deciduous trees (up to 75 feet tall) and shrubs (6 to 15 feet tall) are members of the birch family and grow from ME to FL and westward to OR and CA. They have flexible, thin tassels hanging down from the ends of branches (catkins) which contain pollen, and clusters of female flowers on the same plant (monoecious). The fruit is a one-seeded nut, with the nuts being used as food and flavoring agents. Hazelnuts are wind-pollinated and shed large amounts of pollen in the spring or earlier, usually around the time when pine and juniper pollen is shed.
Pollen grains of Corylus are generally isopolar, suboblate to oblate or oblate-spheroidal and contain 3 pores. The pollen is faintly aspidate and the annulus is slight.
Pollen grains of Corylus vary in size from 20-25 x 26-28 micrometers.
The shaded areas on the map indicates where the genus has been observed in the United States.
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