Pollen grains of the Ixeris chinensis complex were examined in order to investigate the geographical distribution and population structure of diploids, triploids, and tetraploids within the complex. Both voucher specimens and herbarium specimens comprising 1,144 plants collected from 79 populations of 69 localities in South Korea were used. Pollen grains of the diploids were 35-40 ㎛ in size, while those of the triploids and the tetraploids were 25-50 ㎛ and 45-55 ㎛, respectively. Most pollen grains of the triploids were aborted and unstained quite irregularly. In dipoids and tetraploids, most pollen grains were stained and size of the pollen grains was rather uniform. Among 1,144 specimens examined, 518 specimens (45%) were diploid, 179 specimens (15%) triploid, and 447 specimens (40%) tetraploid. Among 79 populations, 42 populations with yellow ligules were diploid, whereas 34 populations with white ligules were triploid and tetraploid. Only three populations showed tetraploidy. Sympatry was found in nine localities. It was found that the diploids and the tetraploids were widely distributed throughout South Korea, and a few triploids occurred in restricted habitats.
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