Correction of Confusions Regarding the Identity and Synonymy of Youngia (Asteraceae: Tribe Cichorieae) in Taiwan

Youngia japonica, the type species for its genus, has the widest distribution in the genus and is invasive worldwide. Recent molecular phylogenetic analysis supported recognition of three ecologically differentiated entities: Y. japonica subsp. formosana, Y. japonica subsp. japonica, and an undescribed morphological variant thought to be a new subspecies in Taiwan. These are the only infraspecific taxa currently recognized in this morphologically variable species. Use of proper names for these taxa and related species is important for future revision of Y. japonica in other regions, for nomenclature and biogeography of the genus, and for activities to control its invasiveness. Careful examination of the holotype of Y. japonica subsp. formosana and relevant literature revealed that the name has long been misapplied to Youngia in mountain ranges in Taiwan; it should be applied to the morphological variant growing on littoral, raised coral reefs in southwestern Taiwan. The misidentified entity is here described as Youngia japonica subsp. monticola. In addition, Y. taiwaniana was treated as a synonym of Y. longiflora (equivalent to Y. japonica subsp. longiflora) in the Flora of Taiwan, but the holotype has achenes with a long beak and does not belong to Youngia. It is here treated as a synonym of Ixeridium laevigatum. A key to Youngia in Taiwan is provided.