Obtaining new records of critically endangered Potamogeton praelongus (Potamogetonaceae) depending on groundwater springs in northern coastal areas of Hokkaido, Japan

Abstract

Potamogeton praelongus Wulfen is an aquatic macrophyte that is critically endangered in Japan. Although it is widely distributed throughout the boreal climatic zone, several European countries also recognize it as an endangered species. In Japan, it was once widely distributed throughout Hokkaido but has disappeared or reduced in abundance at its known locations. During 2020–2021, we discovered five new locations of this species in Wakkanai-shi and Sarufutsu-mura, Northern Hokkaido. Growing conditions must be suitable for this species in three of the five locations as it is present with several reproductive shoots or is widely distributed in source pond or lake. However, conditions were poor in the other two locations because few shoots were found or plants were observed only in 2020. Environmental conditions in the new locations were similar to those reported in Europe and North America. In three of the four locations at Wakkanai-shi, P. praelongus was distributed mainly along the eastern shore facing sand dunes, suggesting that the distribution of this species depends on groundwater springs flowing from sand dunes. Further populations may be discovered in the future by intensively surveying areas near springs since many sand dune lakes and similar environments are present in Hokkaido.