Fraxinus Pollen

Fraxinus (ash) is a genus of trees that is widespread in North America, Europe and Asia. Distinguishing features include pinnately compound leaves and samara type fruits. Four Fraxinus species occur in Oklahoma with F. pennsylvanica the most widely distributed. 

The pollen grains are 20-28 µm in diameter and are usually tetracolpate; however, anywhere from 3 to 6 colpi can occur. The photo below shows tetracolpate and pentacolpate pollen. The colpi are short and the exine is finely reticulate. In Tulsa the Fraxinus pollen season starts in March and peaks in April.