Most species of ash are major offenders in spring pollinosis. Ash is also known to cross-react with olive pollen, which is strongly allergenic.
Ash trees are found mainly in the eastern and southeastern areas of the U.S. Most species bear male and female flowers on separate trees. Flowering ash, Fraxinus ornus, bears bisexual flowers, each containing male and female reproductive organs. The greenish yellow flowers first appear in early spring and are followed by winged seeds that drop in the fall. Ash can grow up to 90 feet tall and resists insects and disease. They are found in areas of full sunlight and well drained soil. Throughout the ages, species of ash have been used for medicinal and nutritional purposes.
Grains are prolate or suboblate to spheroidal and 3-(4)-(6)-colpate. The sexine is typically reticulate.
Pollen grains are 26-28 micrometers.
The shaded areas on the map indicates where the genus has been observed in the United States.
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