Apple cactus

Cereus peruvianus, is a large erect, thorny columnar cactus found in South America . It is an unexplored, underutilized cactus, grown only as an ornamental plant, even though it produces attractive, edible fruits, which are known as pitaya in Latin America. The nocturnal flowers remain open for one night. The fruits are thornless and vary in skin color from violet-red to yellow. The flesh, which is the edible part of the fruit, is white and contains small, edible, and crunchy seeds. Fruits of a number of other columnar cacti, also belonging to the subfamily Cactoideae, tribe Cereeae, are known to be of economic significance for native use in South America.

It´s also called the computer cactus, because it can absorb computer radiations.