Picture of an Apia pollen grain, from the carrot family (left) and a Tilia, or basswood, pollen grain (right).

The tricolporate pollen grain is perhaps the most astonishing. These grains not only have three colpi, but also a central pore in each colpus. In this case the pore provides the emerging pollen tube a point of germination during pollination. Variations in the structure of the surface of the grain in addition to pore features of tricolporate grains are useful taxonomic elements. Tricolporate pollen grains can be found in the fossil record from the Upper Cretaceous to recent.