endexine

The Ostryopsis-Carpinus-Ostrya subclade is defined by staminate flowers without a perianth, operculate pollen apertures with endexine not thickening at apertural region, a base chromosome number of 8, and a plicate leaf vernation pattern.

It is placed at the base of the Coryloideae because it shares primitive characters with the Betuloideae such as bisexual inflorescences, staminate flowers with a perianth, a haploid chromosome number of 14, and nonoperculate pollen apertures with thickened endexine.