Various marsh plants grow in the marsh plant community in the Sengokuhara area. It was designated as a National Natural Treasure because its value in phytogeography was recognized.
It is a marsh plant community that developed in the Sengokuhara marsh, which is the trace of a crater lake (a lake that forms in a volcanic crater) of the Hakone Volcano. The plant community is located inside the Fuji Hakone Izu National Park and became a designated National Natural Treasure after the recognition of its academic value in 1934. A natural condition of low temperature and high humidity is kept throughout the year, so various marsh plants, such as Hakone phragmites, Hosta longissima, and Isachne can be seen. Iris ensata, which blooms in mid-July, is especially popular. In the adjoining Hakone Botanical Garden of Wetlands, in addition to most of the plants that bloom in this wetland, you can also see the marsh plants from all over Japan. It is about 28 minutes on a Hakone Tozan Bus toward the Kojiri Togen-dai terminal when leaving from the Hakone Tozan Railways Hakone Yumoto Station. Get off at the Sengoku bus stop.