Peruvian apple cactus, Cereus repandus (syn. Cereus peruvianus). the Peruvian Apple Cactus' cylindrical gray-green to blue stems can reach 10 metres (33 ft) in height and 10–20 cm in diameter. The nocturnal flowers remain open for only one night. The fruits, known locally as "pitaya" , Olala (only in some places of Bolivia) or Peruvian Apple, are thornless and vary in skin colour from violet-red to yellow.