Firs produce very large amounts of pollen annually in the spring and early summer, but have been reported to have little allergenic importance.
Firs are evergreen trees with a dense, compact pyramidal crown and upright cones. They prefer a cool moist climate. Nine species are native to North America and reach a mature height from 60 to over 250 feet. The needles, retained for more than two years, are usually flat with rounded tips and range from 1/2 to over 2 inches long. Cylindrical, upright cones (usually referred to as pine cones), or flowers, are located on upper branches.
Pine grains are large due to their sacs or bladders, which make them one of the easiest pollen grains to identify. These sacs also allow them to be carried great distances by the wind. Among winged grains, the body is subspheroidal to broadly ellipsoidal. The bladders are generally reticulate or occasionally smooth.
Abies pollen grains can be as large as 160 micrometers.
The shaded areas on the map indicates where the genus has been observed in the United States.
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