Cephalocereus senilis

Native to Mexico, this columnar succulent cactus grows in dry shrublands and limestone canyons and can reach about 50 feet tall in the wild. Its long white hairs are modified spines that reflect sunlight and insulate the stem from heat and cold. Sharp central spines remain hidden beneath the soft covering, which thins with age. Plants may take 10 to 20 years to flower. The flowers open at night, followed by rose-colored fruits whose seeds are dispersed by birds. Wild populations are endangered, partly because plants have been collected for sale. Photographed in Colombia.