24.09.2014
The homeland of cacti is considered to be South America and part of the North. Evolutionarily, cacti as representatives of the flora world appeared about 40 million years ago. They belong to the succulent plant family. The thorns appeared not as a decorative element, but with meaning. They have evolved over the centuries and turned into a real organ of survival.
In the main thick stem of the cactus, a strategic supply of nutrient moisture is concentrated. Another feature of the cactus is the incredibly long roots that go underground and take up an impressive radius of the surface in their growing area. Therefore, they can collect life-giving moisture over a fairly large area. Do not think that it is not common for cacti to have leaves, as all plants we know. It's just that the function of the leaves is performed by these very thorns - a modified version of the leaves. The spines are based on a material similar to organic matter - chitin.
Cacti abandoned the leaves of the usual shape for us for a completely objective reason. As a rule, cacti grow in arid places, and wide leaves would become completely irrational and evaporate precious water in large quantities. Part of the function of the leaves was taken over by a thick, fleshy trunk. On its surface there are very thin stomata, which, if necessary, open their pores and absorb carbon dioxide necessary for photosynthesis.
Another unique feature of the thorns is that small droplets of water are electrostatically attracted to them. Therefore, it does not always need rain for a cactus to drink. In the climate where cacti exist, the temperature fluctuates quite strongly. Dew forms steadily in the air, which is a constant source of moisture for cacti.
In addition to the role of water harvesters, thorns also perform a defensive function. Few of the flora and fauna have adapted to survive so successfully in the desert dunes, and many animals would gladly feast on such a succulent plant. And it is here that thorns stand up for protection, with which no animal can cope. Thanks to the thorns, cacti are able to be reproductive. The spines secrete nectar, which attracts insects, which act as pollinators.
Curiously, the length of the thorns depends on the climatic conditions. The milder the climate, the less frequent the thorns. But they are quite long, because they have only a protective function. The drier the climate, the correspondingly more thorns on the trunk of the cactus. The thorns contain a large amount of mineral salts and calcium carbonate. So, in order for the thorns to grow in the soil, there must be a sufficient amount of calcium. That is why it is necessary to add old plaster or marble chips to the ground for growing cacti.
Think only for self-defense? But no. Their task is reduced not only to this, it is much broader and more interesting. Let's go over the thorns of cacti together and briefly familiarize ourselves with their functions.
Their thorns are of a huge variety. There are sharp, like needles, while long and short. Curved and hooked, hard and soft, radiant and intertwined in glomeruli, feathery and hairy, more like down. All varieties can not be listed. But, regardless of their external structure, they play a primary role in the life of plants of the Cactus family.
They primarily serve to absorb moisture. Indeed, in those places where these extraordinary plants grow, for long months, and sometimes years, there is no rain. As a rule, in deserts there is a sharp temperature drop during the day. At the end of the night, there may be only a couple of degrees of heat, and in the middle of the day the air heats up to 50 degrees. Naturally, under such conditions, there is an intense condensation of water vapor with the formation of abundant dew. It is the dew that serves as the main source of moisture for cacti.
Mammillaria roseoalba has strong protection ...
Cacti are able to absorb water over the entire surface of the stem, but the thorns do this especially intensively. They are modified leaves resembling microscopically thin tubes that actively absorb the slightest moisture. Yes, you can't get drunk with one drop. But there are thousands of thorns on one adult cactus! And each one gets her own drop of dew in the morning. As they say, the world is on a string, i.e. drop by drop, so I quenched my thirst.
Of course, thorns also serve to some extent for protection. But, on reflection, it is easy to guess that in those places where it rains every few years, animals are unlikely to be able to live. Therefore, there is not much to defend against. In such areas, cacti grow with soft and thin thorns, which do not pose a particular danger.
Miracle in feathers - Mammillaria plumosa
Cacti with large and sparse thorns, absolutely not covering the stem, are inhabitants of grassy places. It is clear that these thorns cannot actively water or protect from the scorching sun. Yes, and there is no need for this when there is a lot of grass and bushes around, giving a blessed shade. And the moisture here is quite enough for a normal life. The dry season is always followed by the rainy season. Therefore, such thorns are quite impressive in size and serve solely for protection from herbivores. Hard and spicy, they permanently discourage the taste of such a cactus.
Another task of the thorns is to protect the stem from the scorching sun. In some species of cacti, the thorns cover the stem so tightly that it is practically invisible. And there are species covered with thick white fluff, reminiscent of luxurious fur. And the white color here is not at all accidental: after all, its ability to effectively reflect light is well known. All this helps to avoid destructive overheating in the sun. And on a cold night, such a fur coat will protect you from the cold, when temperatures are not uncommon in these places.
The thorns also serve as decoration to attract cactus enthusiasts. I know it sounds funny, but cactus lovers will understand me. For the variety of shapes, sizes and shades of cactus thorns is simply stunning. Here are just a few examples. The spines-feathers of Mammillaria plumosa cannot but admire - this beauty is simply beyond competition!
Mammillaria lasiacantha can showcase a whole group of plants with feathery spines. What does it look like? Thin rays of numerous spines radiate from areoles, each of which individually resembles a feather in its structure.
And Mammillaria bocasana in her white down coat - just the very charm, Snow Maiden, lost in hot latitudes. By the way, about the snow. Impressive is Mammillaria egregia, perfectly covered with snow-white spines that resemble delicate snowflakes. I think these descriptions are enough to imagine the unique beauty of these creatures.
The world of cacti is large and varied. For centuries, the process of adaptation of these amazing plants to extreme climatic conditions that arose in their habitats has been going on. And as a result, these plants, having neither branches nor foliage, were able to learn how to live and successfully solve the problem of obtaining, accumulating and rational use of life-giving moisture every day. I think they are worthy of our admiration.
Irina Lukyanchik
Original post and comments on
According to legend, a rose once celebrated its birthday. Various plants were invited to the holiday, among which there was a cactus. The prickly friend did not have a present, so he gave the rose his needles. And the rose, in turn, thanked the cactus with a beautiful bud, which blooms once a year, on his birthday.
What are thorns
In most sources, you can find the theory that the thorns of a cactus are modified leaves. Chlorophyll, which is found inside the spines at a certain stage of their development, serves as evidence. But nevertheless, it is more correct to assume that the thorns are modified renal scales.Speaking of which, most people imagine something prickly and sharp. Meanwhile, in nature there is a variety of species of this plant, which can be found specimens with spines in the form of wire, hair, feathers, soft bristles and paper ribbons.
What are thorns for?
Thorns are a survival tool for the cactus. First, they are protective. Large sharp needles scare away herbivores. The spines in the form of thin and short hairs dig into the skin for a long time, discouraging any desire to touch the plant again. However, the protection of thorns is not limited to. For example, the Mammillaria plumosa cactus is covered with white feathers. He needs no protection, so high in the mountains. Feathers protect the plant from overheating, forming a kind of umbrella over it. And on cold nights, they serve as a fur coat for a cactus.In especially arid regions, where rains have to wait for several months, thorns serve as a store of moisture. They are able to absorb water from the air, keeping it inside. This is confirmed by experience: if you remove the cactus from the soil and place it on a dry napkin, the plant will continue to grow, consuming internal moisture reserves. Static tension attracts the smallest particles of water that are contained in morning fog or dew. At the end of the thorn, a drop of water is formed, which is absorbed by the plant. If the “storage” in the needle is full, water flows down the stem to the roots of the cactus in thin streams.
Some types of cacti continue their genus with thorns. For example, Cilindoropuntia has many processes covered with tenacious spines. With them, the plant clings to the wool of approaching animals, which, in turn, transfer shoots to other areas. There are also species in which "hooks" are located on seeds and fruits. And there are specimens that have nectar-bearing spines. This is how the plant attracts pollinators.
The main functions of the leaves are photosynthesis and water evaporation. To perform these functions most effectively, the sheet must have the shape of a plate, that is, it must have a large surface and be thin. These are the leaves of most plants. However, in some plants, the leaves have changed (underwent changes) during evolution and become unlike ordinary leaves. The reason for this phenomenon is that the leaves have begun to perform other functions unrelated to photosynthesis and evaporation.
The leaves of a number of plants in arid habitats have mutated to thorns... Such leaves, on the one hand, almost do not evaporate water, on the other hand, they protect plants from being eaten by animals. Examples of plants in desert areas with thorns are various cacti. Their photosynthesis takes place in the cells of a thick stem located closer to the surface. Water is also stored in the stem. Thus, the leaves modified into thorns lost both of their main functions (photosynthesis and evaporation), but instead began to perform a protective function.
Thorn leaves can be observed not only in desert and semi-desert plants. Barberry, rose bushes, rose hips, etc. have thorns. However, in these plants, not all leaves are transformed into thorns, but only some. Moreover, the function of thorns here is the same as that of cacti - protection from being eaten by animals.
The leaves of other plants in arid habitats have adapted to the lack of moisture in a different way. So the leaves of aloe and agave changed into thick and juicy formations in which water is stored... And to reduce evaporation, such leaves are covered with a waxy bloom, hairs, and have fewer stomata. In this case, the leaves have changed so that they have not lost their main functions, while acquiring an additional one - water storage.
There are plants whose leaves are modified into antennae... With these antennae, the plant clings to the support and is held in an upright position. Examples of tendril plants are peas, rank, vetch, and other legumes. In peas, the upper parts of the leaves are turned into antennae.
Insectivorous plants exist in nature. Their leaves are mutated into peculiar trapping apparatus... When an insect sits on a leaf of a sundew plant, it sticks to it, since the leaf is covered with hairs that emit a viscous mass. After that, the hairs and the sheet itself are curled up. Inside the formed cavity, the insect is digested due to the enzymes secreted by the leaf. Sundew from the insect assimilates nitrogen-rich organic substances. It is because of the lack of nitrogen and other trace elements in their habitats that the sundew leaves acquired such a specific function.
Another leaf modification is scales... In this case, the scales are different, since they perform different functions. For example, in an onion in a bulb, the leaves are turned into juicy scales, in which a supply of nutrients is deposited. Other scales cover the kidneys. In this case, they perform a protective function.
* This work is not a scientific work, it is not a final qualifying work and is the result of processing, structuring and formatting the collected information intended for use as a source of material for self-preparation of educational work.
Cacti are perennial succulents of the cactus family. Mostly inhabitants of deserts and semi-deserts of the American continent.
The leaves of cacti are reduced and replaced by thorns in most species; the stems are capacious water reservoirs. All cacti have areoles (metamorphosis of the axillary bud), from which flowers develop, the "babies" of cacti grow. The peculiar appearance in combination with very beautiful flowering has made these plants very popular among indoor florists. The following species and groups of species are recommended for indoor culture.
Peyrescias have true leaves and grow into large shrubs, often serve as rootstocks for grafting cacti with weak roots on them.
Opuntia are characterized by lozenge-like articulations of the stem and areoles, on which, in addition to thorns, very sharp small bristles (glochidia) develop, which easily pierce the skin and clothing. However, they are often very decorative (for example, in finely pubescent prickly pear varieties).
Cereus are distinguished by columnar faceted stems, in different species they are originally pubescent with long or short hairs, or naked and bluish (Cereus, Cephalocereus, Espooa, Oreocereus, Lemereocereus, Trichocereus).
The group of "black" cacti encompasses a wide variety of genera, which are characterized by a rounded shape and many thorns (hence the name). For breeding in rooms, you can recommend Echinopsis, Echinocactus, Echinocereus, Rebutia, Aylostera, Lobivia and Pseudolobivia, Parody, Gymnocalycium, Ferocactus, Hamatocactus and many others.
Mammillaria - a group of papillary cacti; differ in a variety of shapes and thorns. In mammillaria, the tubercles (papillae) are arranged in a spiral around the stem, and flowers appear between the areoles on the tubercles.
Unlike the above species, epiphyllum, ripsalis, epiphylopsis, ripsalidopsis and zygocactus are forest cacti. Most of them are epiphytes, so in room culture they develop better when grafted (for example, on peiresque). These are shade-loving plants, they do not tolerate direct sunlight. In winter, they require constant moisture. They should be planted in loose humus soil mixed with sand and coal.
All desert cacti can be cultivated in soil composed of sod and leafy soil with the addition of river sand, fine bricks or shards, chalk and charcoal. They are light-loving plants, they need the maximum amount of sun and grow very well outdoors. In winter, cacti should be kept in a cold (-6 degrees to -8 degrees) and always dry place. From October to March, during cold wintering, cacti should not be watered, then they bloom intensively. The best way to water is to immerse the plant pots in the water until the air bubbles stop, then dry them well. The bottom of the pot must be covered with a layer of small shards by 3-4 cm. Young plants have a higher need for moisture, so in winter they need to be watered once a month and make sure that the earth does not dry out and turn into dust. It is difficult to dry adult cacti, and they easily rot from excess water. Reducing watering in winter still does not give the cactus the desired dormant period.
This requires a low temperature, which is easy to achieve by separating the window sill with the cacti on it from the room with glass or plastic wrap.
Sowing cacti requires special attention. It is necessary to sow the seeds in washed river sand, mixed in half with leafy soil, slightly pressing the seeds. Until the emergence of seedlings, it is advisable to keep crops at a temperature of 25-30 degrees and spray only from a spray bottle. At first, the crops must be covered with glass. Small seedlings should be dived several times so that they develop better. In the first year, they should not be overdried, kept in too bright sun or in drafts.
It is easier to propagate cacti by cuttings. Cuttings should be cut with a sharp knife, sprinkled with sulfur or charcoal and left to dry for 3-4 days. Cuttings should be rooted in washed river sand (preferably heated). As soon as the roots are formed and the cuttings begin to grow noticeably, they can be planted in a small bowl. 3-5 days before transplanting, you should stop watering the cacti so that the earthy lump dries up and the earth easily separates from the roots. After transplanting, the plant must be placed in the shade and not watered for 5 days, so that the roots accidentally wounded during transplantation do not rot. The best time to transplant is spring. In order not to prick your hands, when transplanting, cacti should be kept with a strip of rather dense paper folded several times.
Adaptation of a cactus to environmental conditions.
Spread. The homeland of cacti is continental and island America. They are found from Canada to Patagonia and Tierra del Fuego and from the Galapagos Islands to the West Indies. The richest species and life forms of cactus are Mexico. In the United States, cactuses are especially abundant in Texas, Arizona and New Mexico, although the natural range of the family covers almost all states, with the exception of Hawaii, where cacti were naturalized after introduction. The thin-branched epiphytic cactus Rhipsalis grows wild in western Africa, Madagascar and Sri Lanka.
Chemistry, Biology, preparation for GIA and USE
It is believed that it was brought there in ancient times by birds or humans.
Origin:The ancestors of cacti were, most likely, rather moisture-loving plants with well-developed leaves, possibly lianas. As a result of geological processes, the climate in the places where ancient cactus plants grow has become much drier. Plants that could not adapt to the changed conditions died out, and cactus survived due to partial or complete reduction of leaves.
Adaptations.
The cactus tries to absorb as much moisture as possible and store it for a long time. And then very slowly consumes it. So, a cactus must increase its volume to store more water, but must reduce its surface to reduce evaporation. It is known from mathematics that the ball is the geometric body that has the largest volume with the smallest surface. Therefore, cacti are most often spherical.
The leaf function is performed by a green stem of a round, squat or elongated cylindrical shape, ribbed, flat like a leaf or elongated like a vine. They took over the main function of the leaves - photosynthesis.
The giant carnegia cactus lives for 150-200 years, sometimes reaching a weight of 7 tons. A wide-spread root system is located at the very surface of the soil. This is probably why there are no other cacti within a radius of 15-20 m. Carnegia's resistance to unfavorable environmental conditions is surprising: for more than a year, for example, it can be without water, and the side shoots continue to bloom even after the main trunk dies off. The trunk of the carnegia is quite dense, and some species of woodpeckers gouge hollows in it, in which other species of birds can nest in the future.
Organisms often adapt to the same environment in different ways. Common and different adaptations of shark and dolphin.
Conclusion: adaptations of organisms appear as a result of the action of the driving forces of evolution (struggle for existence, natural selection, hereditary variability). Thus, natural selection of their entire variety of undirected hereditary changes selects and fixes only those that provide the population or species as a whole with optimal adaptations to given conditions of existence ...
The relative nature of fitness.
The adaptation of organisms to the environment is developed in the process of long historical development under the influence of natural causes and is not absolute, but relative, since the conditions of the environment often change faster than adaptations are formed. Corresponding to a specific habitat, adaptations lose their meaning when it changes. Proof of the relative nature of fitness can be the following facts: protective devices against some enemies are not effective against others (for example, poisonous snakes, dangerous for many animals, are eaten by mongooses, hedgehogs, pigs); the manifestation of instincts in animals may turn out to be inappropriate (moths collect nectar from light flowers, clearly visible at night, but they also fly into the fire, although they die at the same time); an organ useful in some conditions becomes useless and even relatively harmful in another environment (membranes between the toes of mountain geese, which never sink into the water); more perfect adaptations to this habitat are also possible.
Adaptation to the environment is of a relative nature, useful only in the conditions in which it was historically formed. When these conditions change, adaptations lose their value or even harm the body.
Where do cacti grow?
Cactus, or simply cacti, are perennial flowering plants. It is believed that they evolved evolutionarily about 40 million years ago. Then Africa and South America were already separated from each other, and North America had not yet joined South America.
Despite the fact that no fossil remains of cacti of those times were found, it is believed that they first originated in South America, and came to the northern continent only 5-10 million years ago.
Where do cacti grow in nature?
To this day, cacti in the wild grow mainly on the American continents. It was from there that they were once transported by people and carried by birds to Europe.
However, representatives of cactus in nature can be found not only in America. Some species have been growing for a long time in tropical Africa, Ceylon and other islands of the Indian Ocean.
Where else do cacti grow: thickets of this plant can be found in Australia, the Arabian Peninsula, the Mediterranean, the Canary Islands, Monaco and Spain. Cacti also grow in the wild on the territory of the former Soviet Union. In most cases, cacti were introduced to these places by humans.
Conditions for the growth of cacti
Basically, cacti prefer steppes, deserts and semi-deserts. Sometimes they can also be found in tropical rainforests. Quite rarely, but they still grow on wet coasts.
In Mexico, cacti grow in wormwood, creosote, and alpine succulent deserts. In high-altitude deserts, cacti are concentrated mainly on the Mexican plateau, as well as in the western and eastern parts of the Sierra Madre.
In what deserts do cacti grow: cacti are quite extensive and densely inhabit the deserts of Peru, Chile, Bolivia and Argentina. 
A rich variety of these plants is noted there.
In which countries do cacti grow?
If we designate the geography of cactus growth by country, the list will be something like this: Mexico, Brazil, Bolivia, Chile, Argentina, USA (Texas, Arizona, New Mexico), Canada, China, India, Australia, Spain, Monaco, Madagascar, Sri Lanka, western African countries.
As ornamental plants, people have learned to grow cacti outdoors almost everywhere, with the exception, perhaps, in the Arctic. As indoor plants, cacti have long populated the entire planet.
