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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 dis-appeared 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 condi-tions 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 or hills, suggesting that the distribution of this species depends on groundwater springs flowing from sand dunes or hills. 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.(c) 2022 National Science Museum of Korea (NSMK) and Korea National Arboretum (KNA), Publishing Services by Elsevier. This is an open access article under the CC BY license (http://creativecommons.org/ licenses/by/4.0/).

A small semiartificial pond, revealing high species richness with respect to the aquatic macrophytes, was studied in the Aomori Prefecture, Japan. The pond had been completely formed ca. 10 years previously after excavation into a wet bog. To identify and evaluate its aquatic macrophyte flora during 2017-2018, we listed the species of aquatic vascular plants and charophytes in the pond and compared this list with those from the natural Japanese lakes using a database of aquatic flora in Japan. Two species were identified by molecular analyses because they lacked any reproductive organs, which were necessary for identifying the species level. We found a total of 57 taxa of aquatic macrophytes including 15 Red List species in Japan or Aomori Prefecture. Comparing the flora list with those from the 66 natural Japanese lakes surveyed since 2001, the pond was ranked fourth in the order of diversity (based on species richness) and rarity (based on numbers of Red List species). Therefore, the pond is an important aquatic environment in terms of aquatic macrophyte conservation in Japan. Interestingly, for a pond with such high species diversity, it is relatively small (0.14 km(2)), semiartificial, and relatively recently formed. (C) 2019 National Science Museum of Korea (NSMK) and Korea National Arboretum (KNA), Publishing Services by Elsevier.