The aquatic macrophyte flora of a small pond revealing high species richness in the Aomori Prefecture, Japan

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 km2), semiartificial, and relatively recently formed.