exine

The exine is the outer layer of the walls of pollen grains and some spores. This layer is composed of sporopollenin, a highly decay-resistant substance. The exine typically features one or more thin areas, known as pores, through which pollen tubes germinate. The pattern of the exine's sculpturing, along with the number and placement of these pores, is characteristic of specific plant families, genera, and species. This detailed sculpturing can aid in identifying ancient plant life and understanding past climates, as pollen is well-preserved in the fossil record. The exine itself can have an outer layer called the ektexine.1234