Avocado (Persea americana), popular as 'butter fruit', is a tree native to Mexico and Central America, classified in the flowering plant family Lauraceae. The name "avocado" also refers to the fruit of the tree with an egg-shaped pit.The pear-shaped fruit is botanically a drupe, from 7 to 20 centimetres long, weighs between 100 and 1000 grams, and has a large central seed, 3 to 5 centimetres in diameter., An average avocado tree produces about 120 avocados annually. Commercial orchards produce an average of 7 tonnes per hectare each year, with some orchards achieving 20 tonnes per hectare. Biennial bearing can be a problem, with heavy crops in one year being followed by poor yields the next. The fruit is sometimes called an avocado pear or alligator pear, due to its shape and rough green skin. The avocado tree does not tolerate freezing temperatures, and can be grown only in subtropical or tropical climates. Propagation and rootstocks While an avocado propagated by seed can bear fruit, it takes roughly 4–6 years to do so, and the offspring is unlikely to resemble the parent cultivar in fruit quality. Thus, commercial orchards are planted using grafted trees and rootstocks. Rootstocks are propagated by seed (seedling rootstocks) and also layering (clonal rootstocks). Avocado must be mature to ripen properly. Avocados that fall off the tree ripen on the ground, and depending on the amount of oil they contain, their taste and texture may vary greatly. Generally, the fruit is picked once it reaches maturity.