Cacti aren't found in German nature because Germany gets very cold and much of the land is mountainous or forest land, so they only exist in greenhouses like those in Grugapark.
Very little water is needed for a cactus plant to survive, which is a great thing because it's difficult to find water in a desert climate! Cacti have adapted to living in dry environments by storing water in case they need to go long periods before it rains and by growing spines to protect themselves from herbivores that might want to eat them. The spines help to prevent water loss, too. In Grugapark, the cacti are taken care of carefully by the botanical garden staff, so they don't have to worry about finding water like a wild cactus would.
Cacti have a built-in defense system because they are usually covered all over with long, skinny spines that keep away predators. You always have to be careful when handling cacti because you don't want to accidentally hurt yourself! Unfortunately, despite their excellent adaptations to their environment, cacti are in fact in danger. A recent study published in the scientific journal Nature Plants has indicated that one third of cacti species might be in danger of extinction because of human activity like illegal over-harvesting for the plant trade.
