Cleistocactus strausii
The cactus prefers free draining soils, strong sunlight, but not high temperatures — in fact it can withstand hard frosts down to -10 °C. In its natural habitat it receives plenty of water during the summer, but almost none over the winter. In cultivation, watering too much in winter often leads to root rot.
Opuntia
The flesh ("mucilage") of the cactus has been found to purify water. A project at the University of South Florida is investigating its potential for low-cost, large-scale water purification.