There are only two species of cultivated rice in the world, Oryza sativa (Asian rice) and Oryza glaberrima (African rice). Both species are annual grasses (except in the tropics, where the plant can be perennial) belonging to the family Poaceae which are cultivated for their grain which is considered a staple food in most parts of the world. Asian and African rice plants are morphologically very similar and can be difficult to tell apart. They have rounded stems (called culms) which are divided into nodes and internodes.
Brown rice and white rice have similar amounts of calories and carbohydrates. The main differences between the two forms of rice lie in processing and nutritional content. When only the outermost layer of a grain of rice (the husk) is removed, brown rice is produced. To produce white rice, the next layers underneath the husk (the bran layer and the germ) are removed, leaving mostly the starchy endosperm.