Xerophilic plants or desert plants

Very thick leaves that in some cases tend to curl, thick stems and a handful of particular contours make these plants the queens of the desert. We talk about xerophilic plants which are also known as desert plants because that is one of their natural habitats.

Conclusion plants that thrive in adverse conditions, with arid and dry climates that require a special adaptation. Read on to find out what these are and how they have adapted to the environment to survive.

What are xerophilic plants?

Xerophytic or simply xerophytic plants are specialized plants, that is, plants that throughout their evolution have developed adaptation mechanisms to withstand adverse conditions in which they live as the typical aridity of the deserts or the difficulty to get water growing on a tree.

This is how over time and as they evolved the different species have become resistant from certain changes. The funny thing is that they may belong to different unrelated familiesThe only trait they share is precisely this ability to adapt. That is why they solve the problems of the environment that surrounds them by developing various strategies. We find xerophilic plants in groups as distant as ferns and allies, cycads, gnetids, conifers, and a large number of monocots and dicots.

What are xerophilic plants?

As we have said before, we find xerophytes in all types of plants, since they are only species that have adapted to drought. Since it is impossible to make a list with all the species that exist, we are going to separate them into several groups:

Succulent plants

They are simply plants that accumulate a lot of water in their tissues. In this way, they can usually go a long time without a supply of water, but this is not always true. Even though the vast majority of succulents are xerophilic, not all are. For example, crassula aquatica it is a succulent plant that lives in humid areas, and belongs to the main family of succulents, Crassulaceae. The gender Glasswort They are also succulent plants that live associated with water, but in this case with salt water (halophytes). Among those that are xerophytes we find again, plants that are not related at all:

Succulent monocots

Within the monocots we can find the family asparagaceae, the main family of monocotyledonous succulents (formed almost exclusively by xerophytic plants) where we find the dragon trees (Dracaena spp.), yuccas (Yucca spp.), The agave (Agave spp.) And other similar plants, as well as other plants with the succulent part buried, such as asparagus (Asparagus spp.) with its tuberous or some bulbous roots.

Another important family of succulents is Xanthorrhoeaceae (that of aloes and asphodel). In the rest of the monocot families, the succulent part tends to be buried, so there is discussion about whether they should be considered succulent or not. In others, like Musaceae o Araceae what they have is an airy parenchyma that accumulates water-saturated air, so there is also discussion, but they are not xerophytes.

Succulent dicots

Within the dicotyledons we have the famous cactus (family Cactaceae), at crassulaceae (family Crassulaceae), at euphorbias (gender euphorbia, although there are succulent species and others that are not), living stones, cat's claw and other aizoaceae (Aizoaceae) and many other families with loose species that are succulents, such as the Senecios and the like (part of Asteraceae), Asclepiadoides, Pachypodium and Adenium (apocynaceae), Etc.

Other succulents

We also found a few succulents among the gymnosperms (plants with seeds but without fruit), specifically the genus Ephedra and some cycads. Although these plants are often ignored when talking about succulents, as xerophytes they are without a doubt, we will talk about them later.

Halophytes

These are plants adapted to living in areas with a high amount of salt. This makes many people think that they also endure drought, but this does not have to be the case. Of course they exist halophytic plants which are also xerophytes, such as Atriplex halimus, Suaeda vera, Tamarix spp., Astrophytum asterias o much of the plants of coastal dune ecosystems, but it is important do not confuse halophyte with xerophyte since the adaptations are different, although they can present both at the same time. Halophytes tend to accumulate salt, which raises their osmotic pressure and allows them to absorb salt water, for which they need mechanisms that allow them to expel it without adding it to their metabolism. In most cases this requires a continuous supply of water, as in mangroves or salicornia. Many of these plants are also succulent but do not tolerate drought.

Epiphytes

All the epiphytes They are plants that grow on top of other trees but get water on their own. This implies that they need adaptations to obtain water from the air. The best known epiphytes are the bromeliads, which have two main adaptations: the large ones place the leaves in the shape of a glass to accumulate rainwater and use it little by little. The smaller ones (Tillandsia spp.) Have hairs on the leaves that capture water from the environment. Curiously, this adaptation allows two species of this genus to live in the Atacama Desert, the driest place on the planet.

Other epiphytes such as mosses acquire a dormant state when there is no water present, activating only when they get wet. A very interesting and unique adaptation is that of the myrmecodia or ant plant, which forms galleries in its thick stem for the ants to use and hydrates itself thanks to their excretions and respiration.

Many others simply obtain their water from the moisture that accumulates in the trunk of the tree in which they are growing and do not need to be xerophytes. In drier climates where there are no epiphytes, it is not difficult to see a xerophyte such as a fig, prickly pear or agave growing in a hollow in the trunk of a tree.

Monocotyledonous

As we have said before, within the monocots there are numerous succulent plants (although not all of them are xerophytic plants), however, there are also many species of xerophytes that are not succulents.

The most typical examples are palms coming from dry climates, like almost all genre Phoenix (where we find the Canarian and date palms), the European palmetto (Chamaerops humilis), the washingtonias (Washingtonia rubusta y Washingtonia will spin), Nannorrhops ritchieana, Hyphaene spp.., etc.

Much of the grasses (family poaceae) are also xerophytes, although they are perfectly adapted to grow also in flooded areas. The main adaptation of many of them is to grow and bear fruit fast, in just the couple of months that they have enough water at their disposal. Others are directly perennial and have a metabolism that allows them to consume very little water, such as grass, pennisetum or feather dusters (Cortaderia spp.).

Dicot

In addition to succulents, here we also find numerous non-succulent xerophytes, such as a large part of the Fabaceae (legumes, such as acacias, false acacias and many mediterranean shrubs and deserts), Lamiaceae (rosemary, thyme ...), Asteraceae (santolina, daisies, sunflowers, ...), Malvaceae (mallows, baobabs ...), Fagaceae (holm oaks, kermes oak, oak ...), Apiaceae (parsley and other umbelliferous), etc. All the mediterranean scrub and much of the Mediterranean forest (excluding pines, which are conifers) is made up of xerophilic dicotyledons.

Gymnosperms

Here we find the most diverse plants. The main groups of gymnosperms are the conifers, the cycads, the gnetids and the Ginkgo biloba. We found xerophytic plants in the first three.

Within conifers, the most important xerophytes are found in families Pinaceae y Cupressaceae, being the pines and the cypresses respectively. The pines (Pinus spp.) are usually all more or less xerophilic, with its needle-shaped and rigid blades to reduce evaporation. In general, stiff-leaved pines tolerate drought better than dangling-leaved ones, but this is not always the case. The main adaptations of cupresáceas are the leaves reduced to scales to minimize the evaporation surface and the deep roots, although only some species are xerophytes, like almost the entire genus Cupressus (cypress trees), the genus Juniperus (junipers and junipers) and some moreOthers such as redwoods (Sequoia, Metasequia and Sequoiadendron), bald cypress trees (Taxodium spp.) and sugis (Cryptomeria japonica) are plants that need a constant supply of water.

In cycads we find mainly tropical plants, with an intermediate aspect between a fern and a palm tree. Some of them, such as gender encephalartos, withstand a great deal of drought with their stiff leaves with spiny leaflets (they are always compound leaf) and their thick trunks filled with water. They can be considered succulent.

Gnetids are quite a diverse and rare group. formed by the unique climbing gymnosperm (Gnetum spp..), the only plant that grows by lengthening its only two leaves (Welwitschia mirabilis) And joint grass (Ephedra spp.). Only the last two are xerophytes, and ephedras can also be considered succulent. Welwitschia is a true desert plant, being endemic to the Namib desert, where it gets water thanks to the dew that accumulates on its two large leaves. In the case of Ephedra, are associated with the Mediterranean area, although we can also find them in some deserts and semi-deserts of North America. It has no leaves, and has green stems that grow in segments.

Spore-producing plants

These types of plants (ferns, mosses ...) are almost always associated with very humid areas, but curiously there are species that grow in deserts. Even those that live in these places are unable to retain water. This forces them to be in a state of rest until the rains come. The typical example is the false rose of Jericho, Selaginella lepidophylla, a clubmoss endemic to the Chihuahuan desert. Most of these amazing plants they grow in the shade of rocks, where the humidity is kept longer after the rains. Nevertheless, xerophilous selaginellas grow on the rocks, where the scorching sun hits them. Much of the fern family pteridaceae It is composed of xerophytic plants that inhabit North American deserts.

Another perhaps less impressive example are the numerous epiphytic mosses that grow in Mediterranean forests. These plants present the same adaptation, they remain dormant dry and apparently dead until the water arrives and they hydrate. They usually grow on the north face of the trees, where the sun does not usually shine and moisture accumulates more.

Adaptation mechanisms of xerophilic plants

To withstand drought conditions, these plants have developed various mechanisms that we can put into two groups:

Physiological adaptations

Some xerophilic plant adaptations are physiological, like the ones they have achieved reduce perspiration through the cuticle or they close the stomata when the heat is excessive in order to avoid massive water losses. There is a special metabolism called CAM that is typical of succulents, although not all have it. CAM stands for Acid Metabolism of Crassulaceae. This name was given because it was discovered in a crassulaceae, but cacti and many other plants have it as well. In short, what they achieve with that metabolism is accumulate energy from the sun during the day and finish photosynthesis at night. In this way they do not have to open the stomata during the day, saving all the water that would evaporate.

They are also physiological adaptations those of ferns and the like, which belong in a dormant state until the rains arrive.

Morphological adaptations

In other cases, the adaptations are morphological and this is where the phenomenon is most observable as it can be seen with the naked eye. Many xerophytic plants have a characteristic morphology either in the whole plant or in some of its parts. It is common for them to have dense twigs, leaves covered with waxes or hairs and thorns in order to withstand extreme sun exposure. In this way, they generate a cooler and more humid area in the center of the plant. Another typical morphology is the plants of spherical or cushion appearance that achieves the same results. Of course, this also includes the swollen leaves and / or stems of succulents to accumulate water. Another very common adaptation is to have sclerophyllous (hard) or needle-shaped leaves to reduce evaporation.

What do you think of the xerophytic plants? With them you can build xerophilous gardens, where once the plants are adapted it is not necessary to water and all the water is used. Although for these gardens, it is best to use native plants.