Rice is divided into japonica rice (such as various glutinous rice) and indica rice (ordinary rice).

Indica and japonica rice

Indica rice: about 20% is amylose. It belongs to viscosity. Indica rice originated in the subtropical zone, planted in tropical and subtropical areas, with short growth period and can mature many times a year in places with long frost-free period. After hulling, indica rice has a slender appearance and low transparency. Some varieties have red skins, such as Redmi from Jiangxi, China. After cooking, the rice is dry and loose. Usually used for radish cake, rice flour and fried rice.

Japonica rice: The amylose content of japonica rice is less than 15%. Planted in temperate and cold regions, it has a long growing period and usually ripens only once a year. After hulling into japonica rice, the appearance is round, short and transparent (some varieties of rice have local white powder). Cooking characteristics are between glutinous rice and indica rice. Used for ordinary rice.

Indica rice and japonica rice are two climatic ecotypes formed by long-term adaptation to different ecological conditions, especially temperature conditions, and there are obvious differences in morphological and physiological characteristics between them. Among the rice producing countries in the world, only China has both indica rice and japonica rice, with a large area and obvious geographical distribution. Indica rice is mainly concentrated in tropical south China and subtropical lowlands south of Huaihe River in China, and its distribution range is narrower than that of japonica rice. Indica rice has the habit of heat resistance and strong light resistance. Its botanical characteristics are slender grain shape, poor rice viscosity, rough and hairy leaves, short capillary on the shell, easy to drop grains, similar to wild rice. Therefore, indica rice is a basic type of cultivated rice evolved from wild rice. Japonica rice is widely distributed, from the alpine mountain areas and Yunnan-Guizhou Plateau in the south to the vast areas north of Qinling Mountains and Huaihe River. Japonica rice has the characteristics of cold tolerance and weak light tolerance, short and round grain shape, strong rice viscosity, little or no hair on leaves, long and dense glume, and is not easy to drop grains, which is quite different from wild rice. Therefore, it can be said that japonica rice is a variety that people gradually adapt to low temperature after introducing indica rice from south to north and from low to high.

Rice was originally a wild swamp herb crop, and its growth characteristics are temperature and humidity tolerance. At present, there are still wild rice in a few places in Southeast Asia. Rice has a strong vitality, and can grow well as long as the soil moisture is saturated or close to saturation. There is a proverb in the south of China: "When it rains, rice grows on the ridge.". Rice does not need to be soaked in water all the time during its growth and development. Long-term flood irrigation in rice fields not only wastes valuable water resources, but also is harmful to rice growth. Therefore, using water scientifically according to different growth stages of rice can not only save a lot of agricultural irrigation water, but also improve rice yield.