Haidai is the Chinese name for Laminaria japonica, a seaweed that was introduced to China accidentally from Japan in the late 1920s. Previously, China had imported all requirements from Japan and the Republic of Korea. It is now cultivated on a large scale in China. It is a large seaweed, usually 2-5 m long, but it can grow up to 10 m in favourable conditions (Figure 51). It requires water temperatures below 20°C. Laminaria japonica grows naturally in the Republic of Korea and is also cultivated, but on a much smaller scale; the demand is lower because Koreans prefer wakame (Undaria pinnatifida).