How did the cactus learn to love desert?

When it comes to surviving in a hot and dry environment, no other plant does better then the cactus. Plants that can go a long time without water in hot and arid places, like deserts, are called xerophytes – xeros, dry and phyton. Cactuses have a whole suite of adjustments, which enables them to live in places where water supplies are extremely rare and precious.

Cactuses have small roots because they need every drop of water the heavens can give! When the very rare and blessed rain comes, their roots absorb the water sooner then the sand would take it or the sun would evaporate it.

Most species of cactuses do not even have leaves because they can dry up way too easy. Instead, the photosynthesis moved to the inside, in their solid trunks. To these species, the leaves changed in a better way to conserve water: scales and spines. Basically, these spines and scales are modified leaves, and they don’t lose water through evaporation.

If you cut a cactus open, you see a juicy, slimy tissue. This is where the moisture is stored for the dry season. The part between the middle circle and under the very green part of the plant, just under the skin, is the part allocated for the water storage and food for the plant. This is a type of spongy parenchyma and can take up to 85% of the plant's volume. This is a major adaptation in the desert.

Because the plant remains completely alive during the dry season and there is no need for it to dry up and lose everything, making it possible for the plant to grow to large sizes.

However, where did these adjustments come from? A newer research on their growth shows that these plants developed their strategies and water-rationing long before they needed it, and only later, their anatomy dramatically changed to the way we know today.

Michael Donoghue and Erika Edwards at Yale University, Connecticut, analyzed the mechanism of preserving water in Pereskia Cactus, a kind of plant that looks like a bush, and it is thought to be the ancestor of the cactuses we have today.

The scientists discovered this also, when they analyzed the DNA of 36 species of cactuses, and they reached the conclusion that Pereskia was the beginning of two types of plants, one of them is the cactuses’ family of today. The second group that originated from Pereskia is also very close related with cactuses, genetically speaking, even though you won’t see that because they don’t look alike from an anatomically point of view.

Donoghue and Edwards (which meanwhile moved to California University, Santa Barbara) analyzed now 17 known species of Pereskia, from both groups, brought from different places of South and Central America . They found that even the species that don’t look like cactuses on the outside, have the same kind of water-preserving mechanisms – mechanisms that are very different from the rest of the plants.

The researchers observed that, for instance, the leaves of some Pereskia plants can store much more water and seem to use another kind of photosynthesis which consumes much less of it.

Because all these physiological characteristics are common to both two groups of Pereskia plants, regardless of the fact that they have leaves or not, and in spite of the fact that the separation between them was made long ago, the scientists reached the conclusion that these adjustments broke out before Pereskia plants separated.

The important conclusion we reach is not that these plants adapted in a wonderful way to the extreme conditions from the desert, but that they were able to enter the desert because they developed, without any particular reason, some characteristics of preserving water. And then, after they learned to live in the desert, they only adapted more and more to the hard and difficult conditions from there and improved the mechanisms of water preserving.

The secret of the superior endurance of cactuses lies in their adaptations. Over the years, over the ages, through natural selection, only the strongest and best adapted species survived. The first law of the "jungle" put the Cactus on the throne as the King of the Desert!