Rice is actually the seed of two particular species of grass: Oryza sativa (Asian rice) or Oryza glaberrima (African rice). Rice is a serial grain and the most popular staple food for a large part of the world population, especially in Asia.
Rice is a monocotyledon and is usually cultivated as an annual plant. In tropical climates however, it can be grown as a perennial and can produce a ratoon crop for as long as 30 years. The edible seeds of the plant (caryopsis) are usually between 5-12 mm (0.20–0.47 in) long and 2–3 mm (0.079–0.118 in) thick.