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This page presents summary of the cacti and also other succulent plants. It describes their key features, exactly how they are adjusted to live in dry environments, and also some of your main ecological roles.

For "profiles" of more than 25 different cacti and cactus types, go to the web links at the bottom of this page, or to the Cactus Gallery.

To see just how cacti are combined with other contents of desert communities, walk to The phibìc American Deserts Gallery.

The cactus family members

The cactus family (Cactaceae) contains around 2,500 species, every one of which (with one possible exception) are found naturally just in the ameri (North, main and south America, and also the Caribbean Islands). The one exemption is the genus Rhipsalis which grows normally in Sri Lanka, Madagascar and East Africa, however it might have been introduced into those areas at part time in history or could have arrived there by chance. In more recent times, cacti have actually been introduced into other countries. The most notable example is the prickly pear (Opuntia) which to be introduced right into Australia and also then spread to become a major poblem in rangelands. Yet we deserve to be confident that the cacti space truly natives of the Americas, whereby this family members of tree evolved and also diverged indigenous other species of flower plant along time ago, because the Cactaceae is not very closely related to any kind of other plant family.

All plant households are identified by the details of their flower parts. In the situation of cacti, the flowers have numerous petals that intergrade through sepals, so the the two space not easily distinguished. The flowers likewise have numerous stamens (male components that have the pollen-bearing anthers) and a stigma (female flower part) that has several lobes. Those are the defining features of a cactus, presented in the images below, also though they are not the features that an initial come come mind when we think the a cactus.


Flowers of an ornamental variety of the cactus Epiphyllum, showing the many-lobed stigma and also the countless stamens.

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Flower the a hedgehog cactus, with many-lobed stigma (green) and also stamens

Adaptations for drought tolerance

Cacti are classic examples of plants that have evolved, supposedly from tropic ancestors, to thrive in settings where water is scarce for big parts of the year. They have swollen stems i m sorry contain water-storage tissues, and the stems have a special waterproof epidermis, usually extended with a waxy cuticle to help prevent water loss. Tree of this type are termed stem succulents. The cacti frequently have extensive root systems, dispersing just listed below the floor surface, so that they can absorb even the fairly small amounts of water that moisten the soil surface throughout light showers that rain. To assist them save water in time of plenty, the tribe of countless cacti are fluted, with ribs so the the stem have the right to expand and contract without damages to the surface ar tissues.

Cacti also have evolved to usage the stems together the key photosynthetic organs, for manufacturing sugars, rather than making use of leaves. In fact, most cacti perform not produce leaves in ~ all. The main exceptions room the species of Opuntia (prickly pears and chollas), which have actually rudimentary leaves in their juvenile stages. Yet even this leaves room cylindrical and fleshy, adapted to resist some water loss, and they are melted in drought conditions.

Ribbed stem that the cardon cactus
Ferocious spines the a barrel cactus
Sun-protective spines of a cholla cactus
Spineless living rock cactus

In location of leaves, cacti have actually special organs referred to as areoles. This are like buds and they are arranged frequently along the ribs the the stem or top top the tips of tubercles (see pictures below). They produce spines which assist to safeguard the stems from being eaten by herbivores. In some cacti the spines space so thick that castle almost fully obscure the underlying stems, shielding the stems from extreme sunlight and also preventing the tree from overheating.

Range that form, and also convergent evolution

Even despite we deserve to instantly recognise many cacti as being cacti, they display a wide variety of forms, each adjusted to particular environmental and also site conditions. Because that example, the huge columnar cacti such as the saguaro and the cardon cactus space conspicuous and also dominant tree in desert regions that experience reasonably high rainfall (up to around 30 cm precipitation every year). This cacti comparison with the plenty of smaller forms - regularly 5 - 15 cm tall - i beg your pardon are uncovered in drier conditions. Among the most unusual of this is the living rock cactus that the Chihuahuan Desert (see picture above). This cactus grows together a rosette that triangular, spine-less tubercles ~ above arid limestone ledges, and also stores both water and nutrients in a fairly deep, turnip-like taproot. That blends perfectly with the limestone rock fragments of its habitat, so the is challenging to view - probably an adaptation to safeguard it indigenous herbivores. Much of the selection of form of cacti can be checked out by going to the Cactus Gallery.

Some other plants, rather unrelated to cacti, space stem succulents that have evolved features resembling those that cacti in bespeak to cope with comparable environmental conditions - a procedure termed convergent evolution. Chief amongst these plants are the African varieties of Euphorbia (the spurge family: Euphorbiaceae). For example, the picture on the left below shows 3 plants, but only the tree on the excessive left is a cactus - the "old man" cactus that the Sonoran Desert. The various other two plants space Euphorbia types from Africa. The 3rd of these plants also has mandrel (see the close-up picture on the right) however they space not like the spines that cacti. When we look at the flower it becomes apparent that they room in a various family - the flower structure is usual of Euphorbiaceae.

A cactus (left) and also two Euphorbia varieties from Africa (centre and also right)

Close-up of flowers on the cactus-like Euphorbia

Several other huge plant family members have occurred fleshy, succulent pipeline to cope with periodic drought conditions, and they bear a superficial same to cacti. These plants are called leaf succulents, rather than stem succulents. One of them is the mesembryanthemum family, and also it consists of the impressive living rock plants (Lithops species) that the southern African and also Namibian Deserts (images below). This plants characteristically grow among pebbles on the banks of dry flow beds, where they are perfectly comouflaged and also where castle receive periodic water as soon as the river beds fill after rains. Each plant consists of a pair of fleshy leaves, exposed only at the surface, whereby the photosynthetic organization are located beneath the patterned "windows" (see life stones). They produce white or yellow daisy-like flower in summer, climate the old pair of leaves shrivels while the water and nutrients within them are took in by a brand-new pair of leaves (or sometimes two pairs) which emerge from the gap between the old leaves.

four living stone plants growing in a pot. Remains of a flower are seen in the tree at the left

flower of living rock plants

Another significant family of leaf succulents - the Crassulaceae - are generally known together the stonecrops. These room rosette-forming plants, which space not have to confined come desert regions - they even occur top top rocky outcrops in cool parts of the world, consisting of Britain.

To find an ext examples that succulents, go to the Succulent Gallery.

Physiological adaptations to drought conditions

Plants that flourish in dried environments confront a significant problem. In order to grow, they should absorb carbon dioxide indigenous the atmosphere and also convert it into sugars (photosynthesis) by utilizing energy obtained from light. Plants gain their carbon dioxide through opening small pores, dubbed stomata ~ above the leaf or stem surface. However opening the the stomata throughout the hot, daytime hrs leads to loss the water from the tissues. The cacti and also many other succulent plants have actually overcome this dilemma by making use of a distinct rebab.netchemical procedure called crassulacean mountain metabolism (CAM) since it was first discovered in tree of the Crassulaceae family. Details that this can be uncovered on another page, however basically these plants open up their stomata through night, as soon as the temperature is cool, and also absorb carbon dioxide which they keep by chemically combining it with an organic link containing 3 carbon atoms, creating a 4-carbon organic acid. Throughout the day, once the stomata room closed, the carbon dioxide is exit from this essential acid and also used come synthesize sugars, utilizing the power of light. This plants do exactly the opposite of normal plants, which open their stomata through day when light is easily accessible for photosynthesis, and also close them at night.

Some other plants of hot atmospheres have developed a further physiological adaptation, called C4 metabolism, i m sorry contrasts through the C3 metabolism of many plants. This is discovered especially in countless tropical and subtropical grasses, including those the the warmer deserts of phibìc America. Details can be found on a separate page.

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Cacti as integral contents of organic habitats

Cacti may be fascinating organisms, yet the inquiry we will certainly ask right here is: how necessary are they as members of the desert community? how do they fit right into the totality scene?

The price is that some of the bigger cacti have the right to be major components of the desert vegetation, and administer food and shelter for other organisms. The big cacti assistance a range of animals such as the specialised cactus bees (which use cactus pollen to feed your larvae), javelinas which each huge amounts the prickly pear pads, and also bats which count on the nectar the cardon, saguaro and also organ pipe cactus throughout their annual northern hike from southern Mexico into northern Mexico and also Arizona. Fruits of the bigger cacti administer food for countless birds, if the plants themselves administer shelter and also nest sites because that woodpeckers and flickers, cactus wrens, curve-billed thrashers, owls and also hawks, etc. There is no these big cacti, there would certainly be significantly less pet diversity. Yet the biggest cacti room confined to the smi-tropical environment of the Sonoran Desert of north America and, apart from the chollas and also prickly pears, the other deserts have much smaller cacti that space minor materials of the complete habitat.

In fact, couple of (if any) cacti can be thought about to be the primary components of desert communities, because almost all cacti rely on the shade and shelter of other plants in bespeak for your seedlings to end up being established and to survive the beforehand years of growth. The evidence of this is checked out in the constant occurrence the cacti under nurse plants, consisting of the major nitrogen-fixing trees and sub-trees of the Sonoran Desert. This helps united state to watch the function of cacti in perspective, and also to recognise the crucial roles that other, less spectacular, plants play in the community structure the deserts.

FOR PROFILES OF separation, personal, instance CACTI OR teams OF CACTI - walk TO:

Cardon Saguaro Prickly pears and chollas
Organ pipeline cactus Barrel cacti Senita (old male cactus)
Candelabra cactus Sour pitaya Chihuahuan Desert cacti
Cholla species Fishhooks and pincushions