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exhibition at the Berkeley Botanical Garden, Farbes and Fibers:
Cacti are good crops for dry areas because they efficiently convert water into biomass. As Opuntia species grow in semi-arid environments, the main limiting factor in their environment is water. They have developed a number of adaptations to dry conditions, notably succulence. The perennial shrub Opuntia ficus-indica can grow up to 3-5m height, with thick, succulent and oblong to spatulate stems called cladodes. It has a water-repellent and sun-reflecting waxy epidermis and thorns for leaves.O. ficus-indica (as well as other species in Opuntia and Nopalea) is cultivated in nopalries to serve as a host plant for cochineal insects, which produce desirable red and purple dyes, a practice dating to the pre-Columbian era. DNA analysis indicated O. ficus-indica was domesticated from Opuntia species native to central Mexico. The Codex Mendoza, and other early sources, show Opuntia cladodes, as well as cochineal dye (which needs cultivated Opuntia), in Aztec tribute rolls. The plant spread to many parts of the Americas in pre-Columbian times, and since Columbus, have spread to many parts of the world, especially the Mediterranean, where they have become naturalized.
(edited from Wikipedia)