The exomorphology of pollen grains of all North American species ofCoreopsishave been thoroughly studied under the SEM for the first time with a view to contributing data to the ongoing studies on generic delimitation betweenBidensandCoreopsis. The grains are echinate, tricolporate, isopolar, radially symmetrical, and spheroidal. The size of the pollen grain is between 16.3#x2013;31.7 #xB1; 15.5#x2013;28.3 #x3BC;m and the length of the spine ranges between 3.5 and 6.8 #x3BC;m. No distinct differences in pollen morphological features between the sections of North AmericanCoreopsiswere found. These results are also compared with previous findings on the pollen grains of AfricanBidens(incl.Coreopsis) and only few quantitative and qualitative differences in exomorphology were detected.
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