A New Northern Limit of Najas minor (Hydrocharitaceae) in Japan

Abstract

Najas minor All. (Hydrocharitaceae), hitherto known in areas south of Aomori Prefecture in Japan, was newly recorded in Hokkaido, which updates its northern limit in Japan. Individuals were found in two lakes in the Tokachi region, eastern Hokkaido: Toyokoro-Onuma lake, located in the back-swamp of the Tokachi River; and Oikamanaito lake, a marine lake on the Tokachi Coast. In the former, only a few individuals were collected, which were identified by molecular analysis and morphological examination. In Oikamanaito lake, individuals were consistently found during field-works in 2018–2019. It is difficult to clarify the process or timing of establishment as there are no previously published data on aquatic flora for these lakes.