Abstract
Yakushima is an island known as a biodiversity hotspot for vascular plants in the Japanese Archipelago. At high-elevation areas of Yakushima, three miniaturized groups of Hypericum sect. Hypericum (Hypericaceae) are known. They are distinguished by gland characteristics of the leaf lamina: Group I having only pellucid glands, Group II with both pellucid and dark glands, and Group III with only dark glands. To further distinguish these three groups, we analyzed the phylogenetics, population genetics, morphology and flow cytometry. Genetic analyses showed that Groups I and III are not closely related and clearly differentiated. In addition, individuals of Group II showed intermediate genetic and morphological characteristics of the other two groups. The three groups also differ in ploidy levels; Groups I, II, and III are tetraploid, triploid, and diploid, respectively. These findings suggest that Groups I and III represent two distinct species that may have independently evolved into miniaturized forms on Yakushima, while Group II represents their F1 hybrids. Based on this evidence, we describe Group III as a new species, H. yaedakense D.Takah. & Yahara, and propose a new combination, H. kiusianum Koidz. var. lucidum (Y.Kimura) D.Takah., for Group I.
