Ulmus Pollen

The genus Ulmus (elms) is widely distributed in Northern Hemisphere forests and is also used extensively in landscaping. Seven Ulmus species occur in Oklahoma. Four species have an early spring pollination period releasing pollen from February to early April, and three species have an early fall pollination season releasing pollen from August through October. American elm (Ulmus americana) has the largest natural distribution in Oklahoma and has been extensively used as a popular shade tree. During the 20th century elm trees have been decimated by Dutch elm disease, a fungal disease spread by bark beetles. Newer elm cultivars are resistant to the fungal pathogen. Although elm populations have declined, the pollen is still an important aeroallergen. 

Individual Ulmus pollen grains are 25-35 µm in diameter, typically have five (4 - 6) pores, and rugulate ornamentation on the exine. The early spring elm pollen season has greater pollen concentrations than the fall season and generally has peak concentrations in late February or early March.