Betula Pollen

Betula (birch) species are common trees in Northern Hemisphere forests and woodlands. River birch (Betula nigra) shown on the left is the only Betula species native to Oklahoma. Both male and female flowers are produced in catkins on the same tree. The female catkins are smaller and less conspicuous than the pendulous male catkins. 

The pollen is triporate with strongly aspidate (volcano-like) pores and and distinct oncus beneath each pore. Pollen size is from 23-28 µm in diameter. Pollen release begins in mid-March and continues to mid-April.