Prickly pear (Opuntia ficus-indica) is the most common cactus in the Mediterranean, and is widely naturalised. It is considered a pest in the drier parts of the Canary Islands and elsewhere, displacing less vigorous native plants. The true leaves fall very early on, and the swollen, flattened parts that make up the bulk of the plant are in fact modified stems. It can be propagated by pushing a small piece into the soil which quickly grows into a thick, dense hedge. The edible fruits are ovoid and 5-9cm long; they are sold in markets and are said to be nutritious. The plant may have been introduced fom the Americas, possibly by Christopher Colombus.
Trees and shrubs of the Mediterranean by Helge Vedel, translated from the Danish by Aubrey Rush (Penguin Guides, 1978), p.39.