"Gasha-moku" (Potamogeton dentatus) belongs to Potamogetonaceae (the Pondweed family). It is a perennial herb that is distributed in Kokuraminami Ward, Kitakyushu City, Kyushu, Japan. It used to be distributed in Kasumigaura, Inba-numa Lake, Tega Pond, Lake Biwa, etc. in Honshu, but the habitat is decreasing due to the progress of water pollution. It is a submerged aquatic plant that grows in ponds and rivers. The stem branches at the top and alternates with narrow ovate leaves. The leaves stand out the reticular veins. The yellow-green spikes appear on the surface of the water from June to September. Once upon a time, it was called "moku" and was used as green manure.