Domesticated rice comprises two species in the Poaceae ("true grass") family, Oryza sativa and Oryza glaberrima. These plants are native to tropical and subtropical southern Asia and southeastern Africa. Rice provides more than one fifth of the calories consumed worldwide by humans. (The term "wild rice" can refer to the wild species of Oryza, but conventionally refers to species of the related genus Zizania, both wild and domesticated.) Rice is grown as a monocarpic annual plant, although in tropical areas it can survive as a perennial and can produce a ratoon crop Rice can grow to 1–1.8 m tall, occasionally more depending on the variety and soil fertility. The grass has long, slender leaves 50–100 cm long and 2–2.5 cm broad. The small wind-pollinated flowers are produced in a branched arching to pendulous inflorescence 30–50 cm long. The seed is a grain (caryopsis) 5–12 mm long and 2–3 mm thick.Rice is a staple for a large part of the world's human population, especially in East, South and Southeast Asia, making it the most consumed cereal grain. Rice cultivation is well-suited to countries and regions with low labour costs and high rainfall, as it is very labour-intensive to cultivate and requires plenty of water for cultivation.Rice can be grown practically anywhere, even on steep hillsides. Although its species are native to South Asia and certain parts of Africa, centuries of trade and exportation have made it commonplace in many cultures.Traditional method for cultivating rice is flooding the fields with or after setting the young seedlings. This simple method requires sound planning and servicing of the water damming and channeling, but reduces the growth of lesser robust weed and pest plants and reduces vermin that has no submerged growth state. However, with rice growing and cultivation the flooding is not mandatory, whereas all other methods of irrigation require higher effort in weed and pest control during growth periods and a different approach for fertilizing the soil.