Junsai (Water Shield) (ジュンサイ)

Junsai (Brasenia schreberi) is perennial hydrophyte. It grows naturally in clear fresh water ponds. It is sometimes grown as it young buds are edible.


Junsai belongs to Cabombaceae. Or it is included in Nymphaeaeceae, and is waterweed whose leaves float on the surface of water as water lilies do.

In Japan it is distributed from Hokkaido to Kyushu and Nansei Islands (Tanegashima Island and the islands of Okinawa), and in some areas it has gone extinct already. Outside of Japan it is distributed widely from Southeast Asia to India, Africa, Australia, and Americas.

It is perennial floating leaved plant. Its leaves are alternate and oval in shape, 5 to 12 mm long, and purple on the back. Leafstalks run the middle of the back of leaves such as shields, in the same way as those of lotus. Its rootstalks are in the mud of the bottom of water. Leafstalks do not come out from here but stems extends close to water surface. In autumn part of the rootstalk stores nutrients to be turion to stay over the winter. Leafstalks sparsely come out from this part and have leaves on the end. Buds on the end of stems and the back of young leaves are slimy, thickly covered with agar mucilage. It flowers from June to August. Flowers are on the end of stems which extend toward water surface, and the diameter is 1 to 1.6 cm. They have three petals and sepals respectively and look like thinner water lily flowers, but do not stand out since the petals are purplish brown.


Young buds covered with agar are valued as material for Japanese cuisine. Junsai is regarded as a local dish of Akita Prefecture, and Mitane Town of Akita has the highest crop.

Vinegared dish
Suimono (clear soup)
Miso soup
Soup (Xi Hu, China)

In Onuma Quasi-National Park of Nanae Town, Hokkaido, there is Junsai Swamp, one of the Onuma main lakes (Nanae Town), and they sell bottled junsai as a special product of the Park.

Junsai is often grown in private ponds and you have to confirm before you collect junsai.


Junsai appears in Manyoshu (the oldest anthology of Japanese poetry) as 'nunawa.'

My mind fluctuates as floating nunawa, it will never reach any shore or somewhere away.

Positioning in terms of protection

Junsai is referred to in the red data book made by local public bodies mentioned below. Though it is common species in Japan as a whole, it has high risk of extinction in some areas and has already gone extinct in some other areas. The main reasons for extinction and decrease include development of ponds and declining quality of water.

[Original Japanese]