What kind of plant is "rush", the raw material for tatami mats?

Rush is a monocotyledonous plant and a perennial.
Another name is rush.
The distribution in Japan is a wet plant that grows in lakes, rivers, wetlands, etc. from Hokkaido to Okinawa, and blooms from May to September.
Rush used for tatami mats has been cultivated in paddy fields. Also, the cultivated tatami mat Rush is usually cut in July.

The main production areas are Kumamoto prefecture, Hiroshima prefecture, Okayama prefecture, Ishikawa prefecture, Kochi prefecture, Fukuoka prefecture, Saga prefecture, Oita prefecture, etc.
In particular, the Yatsushiro region of Kumamoto Prefecture has the highest production in Japan, accounting for an overwhelming share of 80% to 90% in the Japanese tatami mat market.

In the olden days, Bizen table using Rush produced in Hiroshima region and Bizen table using Rush produced in Okayama region were famous as luxury products, but now Rush produced in Yatsushiro is also used for luxury products. It has become like.