How can succulents go days without water?

This cactus is an example of a succulent. Cacti are the largest family of succulents, but they aren't the only ones -- close to 30 plants families have succulents around the super table. See more pictures of cacti.
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From wriggling amoebas to roving rhinos, delicate dandelions to majestic redwoods, everything that lives on Earth needs one superstar element to survive: water. Luckily for us, water is abundant on the planet -- the catch is that it's not evenly distributed.

If life is anything, it's tenacious. Over time organisms have evolved to fill even the most barren ecological niches. The microbes commonly referred to as extremophiles, are a great example. Thermophiles like it nice and toasty, halophiles think super-salty is the way to go and nothing will do for psychrophiles but the big chill.

In the case of plants, there's a special set known as xerophytes, which have evolved to survive in climates where water is extremely scarce. And among the xerophytes, we find an assembly of plants called succulents. The term succulent (and xerophyte for that matter) doesn't denote a traditional taxonomic group, however. Rather, succulents are diverse plants share common adaptations for making the most of every bit of water they can get. It's also important to note that the line between succulent plants and ordinary plants is not cut and dry. On a short-term basis, all plants are generally able to do what succulents are so renowned for -- it's just that succulents take things to a whole other level.

­­The succulent that probably springs to mind most readily is the cactus, although there are succulents in a wide variety of plant families. You might imagine succulents only inhabit wind-swept arid desert regions where little else can grow, but that's not the case. Succulents are a­bundant in a variety of locales. You can find them growing in the upper reaches of tropical rain forests, rooted to high-rise patches of moss or bark where the competition for water is fierce. You can find them in lofty mountainous regions where cold weather, severe winds and rocky soil make finding moisture a challenge. You can even find them on the shores of salty bodies of water, where brackish conditions hinder normal botanical water routines.

It's worth noting, too, that succulents aren't superheroes -- there are some regions where the desert conditions are so extreme that only the most hardcore xerophytes can survive. While succulents are champions at water collection and conservation, most need at least a few inches of rain annually to get by. There are a few other exceptions as well. In some places, deserts spring up too quickly for local plants to evolve and in others, the plants just find other ways to adapt.

Now that we've got the basics down, continue on to the next pages for the dirt on how these plants are able to get by with such tiny amounts of water.