Pollen morphology of North American Coreopsis (Compositae — Heliantheae)

Abstract

The exomorphology of pollen grains of all North American species of Coreopsis have been thoroughly studied under the SEM for the first time with a view to contributing data to the ongoing studies on generic delimitation between Bidens and Coreopsis. The grains are echinate, tricolporate, isopolar, radially symmetrical, and spheroidal. The size of the pollen grain is between 16.3–31.7 ± 15.5–28.3 μm and the length of the spine ranges between 3.5 and 6.8 μm. No distinct differences in pollen morphological features between the sections of North American Coreopsis were found. These results are also compared with previous findings on the pollen grains of African Bidens (incl. Coreopsis) and only few quantitative and qualitative differences in exomorphology were detected.