Natural Distribution and Habitat of Koelreuteria paniculata Laxm. (Sapindaceae) in Japan and Its New Form

Abstract

Koelreuteria paniculata Laxm. has been regarded in different views as a species imported from China or as an indigenous species to Japan. Based on extensive field work we found many natural populations of the species in northeastern Miyagi Prefecture. We recognized K. paniculata is wild and native in these habitats. Natural populations of the species occupy an almost uniform condition. Their habitats are mostly in natural Zelkova serrata forests developed on stony and poorly soiled cliffs facing east to south along coasts and along the river Kitagami-gawa in Miyagi Prefecture. Wild populations of K. paniculata in Japan are also recognized as indigenous based on examination of herbarium specimens and references or records of the species in each localities. They occur sporadically in the following prefectures from northeast to west: Aomori, Akita, Iwate, Miyagi, Yamanashi, Nagano, Ishikawa, Fukui, Hyogo, Shimane, Yamaguchi and Nagasaki (Tsushima). Flowers of K. paniculata are bright yellow, but we found plants with pale yellow flowers in four populations in Miyagi Prefecture. The form is recognized at the rank of forma as K. paniculata f. miyagiensis H. Ohashi & Yu. Sasaki.