Cinnamomum cassia is the dried bark of cassia, which is a small, bushy, evergreen tea, 18-20 meters high and 40-60 cm diameter with a straight and cylindrical trunk and grey-brown bark, 13-15 mm thick when mature. Cassia occurs mainly in South China, Vietnam, Laos, and Myanmar. In India, only a few plants are available. Cassia is a light-demanding tree, slightly shade-tolerant when young, preferring cool and wet conditions.

Dried Cassia bark is the spice. The essential oil is called cassia cinnamon oil. Apart from its use as a spice, it is a well-known medicine reinforcing yang, the body fire. Guizhi (dried twig of cassia cinnamon) is collected in spring and summer and dried in the sum or in the shade used in decoctions, has analgesic and antipyretic properties.