The genus Carpinus is represented in Great Britain by Carpinus betulus, the Hornbeam. This is an average sized tree that if unimpeded can grow with a neat rounded shape tapering to the top. The leaves are small, quite tough and rather like a dark crinkled elm leaf. Although this tree is not considered a native to Ireland, it is worth including for two reasons.
As with several other supposedly non-native trees in Ireland, it may be that the presence of very small numbers of fossil pollen indicates a low level population of natives, or indeed wind borne pollen from elsewhere. The fact that Hornbeam is more at home in SE England with the more continental climate suggests it is less likely to be an Irish native. Godwin cites the existence of Hornbeam through various of the interglacials in southern Great Britain, in more easterly regions.
The pollen has characteristics that make it useful in palynology to be familiar with it, for it bears certain similarities to Alnus, Betulus, Corylus and Myrica. Erdtman however did not consider that there is enough distinction between the pollen of the families Corylaceae and Betulaceae to justify separating them. The necessity of identifying fossil grains does justify this though.
The pollen grains may bear between four and six, or even more pores, in a configuration reminiscient of Alnus. Fresh pollen grains appear dented and collapsed and often have little regularity in their shape. The grains when acetylated are generally almost circular, or oblate pentangular. The pores are as visible and prominent as breaks in the exine as the other genera mentioned, but with differing characteristics. The pores protrude ony slightly, if at all, and are not vestibular. The break in the exine at the pore is more ragged, less defined , and certainly not similar to the 'snakes head' style. The outer surface of the grains are scabrate or microscabrate.
The tree flowers early, before the leaf buds open, flowering in March, with seperate male and female catkins on the same plant (monoecious). Male catkins produce profuse amounts of pollen from individual florets.
The catkins, florets, and pollen grains shown below are from a cultivated Carpinus, species unknown. Pollen grain sizes are between 27 and 35 microns. 'Washed' grains have had pollenkitt removed by dipping in alcohol or silicon oil. It is noticeable that some pollen grains break or burst open upon acetylation - see some of the later images.