Micromorphological and cytological comparisons betweenYoungia japonicaandYoungia longiflorausing light and scanning electron microscopy

The genusYoungiaCass. is taxonomically complex and widely distributed in East Asia. Despite the high diversity of species, only two species,Youngia japonica(L.) DC. andYoungia longiflora(Babc. & Stebbins) C.Shih, are currently found in Korea. Among them,Y. longiflorawas once recognized as a subspecies ofY. japonica. However, based on chloroplast and nuclear DNA sequences, as well as morphology,Y. longiflorawas found to be a distinct species. Here, the two KoreanYoungiaspecies were analyzed using scanning electron microscope and light microscope for chromosome number, pollen, cypselae, and leaf micromorphological characters to evaluate if the examined characters are informative for taxonomy. Pollen morphology is described, and the micromorphological characters ofY. longifloraare described for the first time. Cypselae and pollen surface ornamentation, as well as trichome morphology and stomatal size varied between the two species.Y. japonicahad longer chromosomes thanY. longiflora, while other chromosomal characters including the localization of the NOR (nucleolar organizer region) were similar. The present micromorphological and cytological results are of great taxonomic value forYoungiaspecies identification in Korea.