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Cactus

2007 Schools Wikipedia Selection. Related subjects: Plants

                       How to read a taxoboxCacti
   Ferocactus pilosus (Mexican Lime Cactus) growing south of Saltillo,
   Coahuila, northeast Mexico
   Ferocactus pilosus (Mexican Lime Cactus) growing south of Saltillo,
   Coahuila, northeast Mexico
                        Scientific classification

   Kingdom:  Plantae
   Division: Magnoliophyta
   Class:    Magnoliopsida
   Order:    Caryophyllales
   Family:   Cactaceae
             Juss.

                                   Genera

   See Taxonomy of the Cactaceae

   A cactus (plural cactus, cactuses or cacti) is any member of the
   succulent plant family Cactaceae, native to the Americas. They are
   often used as ornamental plants, but some are also crop plants.

   Cacti are distinctive and unusual plants, which are adapted to
   extremely arid and hot environments, showing a wide range of anatomical
   and physiological features which conserve water. Their stems have
   expanded into green succulent structures containing the chlorophyll
   necessary for life and growth, while the leaves have become the spines
   for which cacti are so well known.

   Cacti come in a wide range of shapes and sizes. The tallest is
   Pachycereus pringlei, with a maximum recorded height of 19.2 m, and the
   smallest is Blossfeldia liliputiana, only about 1 cm diameter at
   maturity. Cactus flowers are large, and like the spines and branches
   arise from areoles. Many cactus species are night blooming, as they are
   pollinated by nocturnal insects or small animals, principally moths,
   bats, and sheep. Cacti's sizes range from small and round to pole-like
   and tall.

Taxonomy

   The family of the Cactaceae, with an age of a few million years, is
   counted as a relatively young plant family, of which no fossil finds
   are known. Within this short time span (short at any rate from a
   geological point of view) the cactuses have undergone a rapid
   development into extremely specialised plants.

   The family of the Cactaceae with approx. 2,000-3,000 species and
   varieties in about 60 genera was originally native to the American
   continent, where their range extends from Patagonia to the
   Canadian–American border. Cacti inhabit the most diverse regions, from
   coastal plains to high mountain areas, from the sub-tropics to the
   deserts. The most dense occurrence of cactuses is to be found in the
   territories around north Mexico and the southern tropic (Argentina and
   Bolivia). The equivalent plants to cactuses in Africa and Australia are
   representatives of the so-called "other succulents". Occurrences of
   cacti outside the Americas are the result of distribution by humans (or
   in very rare cases by migrating birds).

Distribution

   Echinopsis spachiana in flower
   Echinopsis spachiana in flower

   Cacti are almost exclusively New World plants. This means that they are
   native only in North America, South America, and the West Indies. There
   is however one exception, Rhipsalis baccifera; this species has a
   pantropical distribution, occurring in the Old World tropical Africa,
   Madagascar and Sri Lanka as well as in tropical America. This plant is
   thought to be a relatively recent colonist in the Old World (within the
   last few thousand years), probably carried as seeds in the digestive
   tracts of migratory birds. Many other cacti have become naturalized to
   similar environments in other parts of the world after being introduced
   by people.

   Cacti are believed to have evolved in the last 30 to 40 million years.
   Long ago, the Americas were joined to the other continents, but
   separated due to continental drift. Unique species in the New World
   must have developed after the continents had moved apart. Significant
   distance between the continents was only achieved in around the last 50
   million years. This may explain why cacti are so rare in Africa; the
   continents had already separated when cacti evolved. Many succulent
   plants in both the Old and New World bear a striking resemblance to
   cacti, and are often called "cactus" in common usage. This is, however,
   due to parallel evolution; none of these are closely related to the
   Cactaceae.

   Prickly pears (genus Opuntia) were imported into Australia in the 19th
   century to be used as a natural agricultural fence and to establish an
   cochineal dye industry, but quickly became a widespread weed. This
   invasive species is inedible for local herbivores and has rendered
   40,000 km² of farming land unproductive.

Adaptations to dry environment

   Some environments, such as deserts, semi-deserts and dry steppes,
   receive little water in the form of precipitation. Plants that inhabit
   these dry areas are known as xerophytes, and many of them are
   succulents, with thick or reduced, "succulent", leaves. Apart from a
   very few exceptions (for example, the genus " Rhodocactus") all
   cactuses are succulent plants, although not all succulent plants are
   cacti. Like other succulents, these cacti have a range of specific
   adaptations that enable them to survive in these environments.
   Pereskia grandifolia: Pereskia is a weakly succulent genus, which also
   possesses leaves, and is believed to be very similar to the ancestor of
   all cacti.
   Pereskia grandifolia: Pereskia is a weakly succulent genus, which also
   possesses leaves, and is believed to be very similar to the ancestor of
   all cacti.

   Cactus have never lost their leaves completely, they have only reduced
   its size so that they will reduce the surface area through which water
   can be lost by transpiration. In some species the leaves are still
   remarkably large and ordinary while in other species they have became
   microscopic but they still contain the stomata, xylem and phloem.
   Certain cactus species have also developed ephemeral leaves, which are
   leaves that last for a short period of time when the stem is still in
   his early stages of development. A good example of a species that have
   ephemeral leaves is the Opunta ficus indicia better known as the
   prickly pear. Cactus have also developed spines which allow less water
   to evaporate through transpiration by shading the plant, and defend the
   cactus against water-seeking animals. The spines grow from specialized
   structures called areoles. Very few members of the family have leaves,
   and when present these are usually rudimentary and soon fall off; they
   are typically awl-shaped and only 1-3 mm long. Two genera, Pereskia and
   Pereskiopsis, do however retain large, non-succulent leaves 5-25 cm
   long, and also non-succulent stems. Pereskia has now been determined to
   be the ancestral genus from which all other cacti evolved.
   Many species of cactus have long, sharp spines.
   Many species of cactus have long, sharp spines.

   Enlarged stems carry out photosynthesis and store water. Unlike many
   other succulents, the stem is the only part of a true cactus where this
   takes place. Much like many other plants that have waxy coatings on
   their leaves, Cacti often have a waxy coating on their stems to prevent
   water loss. This works by preventing water from spreading on the
   surface and allowing water to trickle down the stem to be absorbed by
   the roots and used for photosynthesis.

   The bodies of many cacti have become thickened during the course of
   evolution, and form water-retentive tissue and in many cases assume the
   optimal shape of the sphere (combining highest possible volume with
   lowest possible surface area). By reducing its surface area, the body
   of the plant is also protected against excessive sunlight.
   Saguaro cactus in Arizona, USA. This species is well known from Western
   films.
   Saguaro cactus in Arizona, USA. This species is well known from Western
   films.

   Most cacti have a short growing season and long dormancy. For example,
   a fully-grown Saguaro cactus ( Carnegiea gigantea) can absorb up to
   3,000 litres of water in ten days. This is helped by cacti's ability to
   form new roots quickly. Only two hours after rain after a relatively
   long drought the formation of new roots begins. Apart from a few
   exceptions an extensively ramified root system is formed, which spreads
   out immediately beneath the surface. The salt concentration in the root
   cells is relatively high, so that when moisture is encountered, water
   can immediately be absorbed in the greatest possible quantity.

   But the plant body itself is also capable of absorbing moisture
   (through the epidermis and the thorns), which for plants that are
   exposed to moisture almost entirely, or indeed in some cases solely, in
   the form of fog, is of the greatest importance for sustaining life.

   Most cacti have very shallow roots that can spread out widely close to
   the surface of the ground to collect water, an adaptation to infrequent
   rains; in one examination, a young Saguaro only 12 cm tall had a root
   system covering an area 2 meters in diameter, but with no roots more
   than 10 cm deep. The larger columnar cacti also develop a taproot,
   primarily for anchoring but also to reach deeper water supplies and
   mineral nutrients.

   One feature distinguishes the cacti from all other plants: cactuses
   possess areoles, as they are known. The areole appears like a cushion
   with a diameter of up to 15 mm and is formed by two opposing buds in
   the angles of a leaf. From the upper bud develops either a blossom or a
   side shoot, from the lower bud develop thorns. The two buds of the
   areoles can lie very close together, but they can also sometimes be
   separated by several centimetres.

   Like other succulents in the families of the Crassulaceae, Agavaceae
   (agaves), Euphorbiaceae (euphorbias), Liliaceae (lilies), Orchidaceae
   (orchids) and Vitaceae (vines), cacti reduce water loss through
   transpiration by Crassulacean acid metabolism. Here, transpiration does
   not take place during the day at the same time as photosynthesis, but
   at night. The plant stores the carbon dioxide chemically linked to
   malic acid until the daytime. During the day the stomata are closed and
   the plant releases the stored CO[2] and uses it for photosynthesis.
   Because transpiration takes place during the cool humid night hours,
   water loss through transpiration is significantly reduced.

Reproductive ecology

   Blooming Echinopsis. The flower opens towards evening and dies the
   following morning.
   Blooming Echinopsis. The flower opens towards evening and dies the
   following morning.

   Some cactus flowers form long tubes (up to 30 centimetres) so that only
   moths can reach the nectar and thus pollinate the blossoms. There are
   also specialisations for bats, humming birds and particular species of
   bees. The duration of flowering is very variable. Many flowers, for
   example those of Selenicereus grandiflorus (Queen of the Night) are
   only fully open for two hours at night. Other cactuses flower for a
   whole week. Most cacti are self-incompatible, and thus require a
   pollinator. A few are autogamous and are able to pollinate themselves.
   Fraileas only opens their flowers completely in exceptional
   circumstances; they mostly pollinate themselves with their flowers
   closed ("cleistogamy"). The flower itself has also undergone a further
   development: the ovary tends to become a completely protected area,
   protected by thorns, hairs and scales. Seed formation is very prolific,
   and the fruits are mostly fleshy, pleasant tasting and conspicuously
   colored. Goats, birds, ants, mice and bats contribute significantly to
   the spreading of the seeds.

   Because of the plants' high water-retention ability, detached parts of
   the plant can survive for long periods and are able to grow new roots
   everywhere on the plant body.

   Some cacti are able to reproduce by budding. These cacti grow on one
   another. While they appear to be one plant they are actually several
   cacti. These types of cacti will survive if separated from the main
   plant. They will take root and start the budding process as the main
   plant.

History

   Carl Spitzweg: The Cactus Lover, c. 1856
   Carl Spitzweg: The Cactus Lover, c. 1856

   Among the remains of the Aztec civilization cacti can be found
   repeatedly in pictorial representations, sculpture and drawings,
   principally Echinocactus grusonii. This cactus, also known as
   "Mother-in-law's Cushion", has great ritual significance - human
   sacrifices were carried out on these cacti. Tenochtitlan (the earlier
   name of Mexico City) means "place of the sacred cactus". The national
   arms of Mexico to this day show the eagle, snake and cactus.

   Economic exploitation of the cactus can also be traced back to the
   Aztecs. The North American Indians exploit the alkaloid content of many
   cactuses for ritual purposes. Today, besides their use as foodstuffs
   (jam, fruit, vegetables), their principal use is as a host for the
   cochineal insect, from which a red dye ( carmine)is obtained which is
   used in Campari or high-quality lipsticks. Particularly in South
   America dead pillar cacti yield valuable wood for construction. Some
   cactuses are also of pharmaceutical significance.

   From the moment of their discovery by early European explorers cacti
   have aroused much interest: Christopher Columbus brought the first
   melocactuses to Europe. Scientific interest in them began in the 17th
   century. By 1737 24 species were known, which Linné grouped together as
   the genus "Cactus". With the passage of time cacti enjoyed increasing
   popularity: sometimes they were of scientific interest only; at other
   times as fashionable plants they enjoyed a real boom.

   From the beginning of the 20th century interest in cacti has increased
   steadily, interrupted only by the two world wars. This was accompanied
   by a rising commercial interest, the negative consequences of which
   culminated in raids on the cactuses' native habitats, resulting in the
   extermination of many species. Through the great number of cactus
   admirers, whether their interest is scientific or hobby-oriented, new
   species and varieties are even today discovered every year.

   All cacti are covered by the Convention on International Trade in
   Endangered Species of Wild Fauna and Flora, and many species by virtue
   of their inclusion in Appendix 1 are fully protected.

   Some countries have a rather contradictory attitude to species
   protection. In Mexico for example to be caught in the act of digging up
   cacti carries a prison sentence, but cactus habitats are destroyed for
   the construction of new roads and electricity lines. To be borne in
   mind here is that some cactus habitats have a total area of no more
   than 1,000 square metres. If this habitat is destroyed, either by
   construction or by plundering, the species growing there is lost for
   posterity if it is endemic (ie, growing in that one spot and nowhere
   else).

Uses

   Echinocactus grusonii is a popular species in cultivation
   Echinocactus grusonii is a popular species in cultivation

   Cacti, cultivated by people worldwide, are a familiar sight as potted
   plants, houseplants or in ornamental gardens in warmer climates. They
   often form part of xerophilic (dry) gardens in arid regions, or raised
   rockeries. Some countries, such as Australia, have water restrictions
   in many cities, so drought-resistant plants are increasing in
   popularity. Numerous species have entered widespread cultivation,
   including members of Echinopsis, Mammillaria and Cereus among others.
   Some, such as the Golden Barrel Cactus, Echinocactus grusonii, are
   prominent in garden design. Cacti are commonly used for fencing
   material where there is a lack of either natural resources or financial
   means to construct a permanent fence. This is often seen in arid and
   warm climates, such as the Masai Mara in Kenya. This is known as a
   cactus fence.

   As well as garden plants, many cacti have important commercial uses;
   some cacti bear edible fruit, such as the prickly pear and Hylocereus,
   which produces Dragon fruit or Pitaya. Opuntia are also used as host
   plants for cochineal bugs in the cochineal dye industry in Central
   America.

   The Peyote, Lophophora williamsii, is a well-known psychoactive agent
   used by Native Americans in the Southwest of the United States of
   America. Some species of Echinopsis (previously Trichocereus) also have
   psychoactive properties.

Etymology

   Prickly Pear is among the most common cacti found in North America.
   Prickly Pear is among the most common cacti found in North America.

   The word cactus is ultimately derived from Greek Κακτος kaktos, used in
   classical Greek for a species of spiny thistle, possibly the cardoon,
   and used as a generic name, Cactus, by Linnaeus in 1753 (now rejected
   in favour of Mammillaria). There is some dispute as to the proper
   plural form of the word; as a Greek loan into English, the correct
   plural in English would be "cacti". However, as a word in Botanical
   Latin (as distinct from Classical Latin), "cactus" would follow
   standard Latin rules for pluralization and become "cacti", which has
   become the prevalent usage in English. Regardless, cactus is popularly
   used as both singular and plural, and is cited as both singular and
   plural by the Random House Unabridged Dictionary (2006).

Selected important genera

     * Acanthocalycium
     * Acanthocereus
     * Acharagma
     * Armatocereus
     * Arrojadoa
     * Arthrocereus
     * Astrophytum
     * Austrocactus
     * Austrocylindropuntia
     * Aztekium
     * Bergerocactus
     * Blossfeldia
     * Brachycereus
     * Brasilicereus
     * Brasiliopuntia
     * Browningia
     * Calymmanthium
     * Carnegiea
     * Cephalocereus
     * Cephalocleistocactus
     * Cereus
     * Cintia
     * Cipocereus
     * Cleistocactus
     * Cochemiea
     * Coleocephalocereus
     * Consolea
     * Copiapoa
     * Corryocactus
     * Coryphantha

     * Cumulopuntia
     * Cylindropuntia
     * Dendrocereus
     * Denmoza
     * Discocactus
     * Disocactus
     * Echinocactus
     * Echinocereus
     * Echinomastus
     * Echinopsis
     * Epiphyllum
     * Epithelantha
     * Eriosyce
     * Escobaria
     * Escontria
     * Espostoa
     * Espostoopsis
     * Eulychnia
     * Facheiroa
     * Ferocactus
     * Frailea
     * Geohintonia
     * Grusonia
     * Gymnocalycium
     * Haageocereus
     * Harrisia
     * Hatiora
     * Hylocereus
     * Isolatocereus
     * Jasminocereus
     * Lasiocereus

     * Leocereus
     * Lepismium
     * Leptocereus
     * Leuchtenbergia
     * Lophophora
     * Maihuenia
     * Maihueniopsis
     * Mammillaria
     * Mammilloydia
     * Matucana
     * Melocactus
     * Micranthocereus
     * Mila
     * Miqueliopuntia
     * Myrtillocactus
     * Neobuxbaumia
     * Neolloydia
     * Neoraimondia
     * Neowerdermannia
     * Obregonia
     * Opuntia
     * Oreocereus
     * Oroya
     * Ortegocactus
     * Pachycereus
     * Parodia
     * Pediocactus
     * Pelecyphora
     * Peniocereus
     * Pereskia

     * Pereskiopsis
     * Pilosocereus
     * Polaskia
     * Praecereus
     * Pseudoacanthocereus
     * Pseudorhipsalis
     * Pterocactus
     * Pygmaeocereus
     * Quiabentia
     * Rauhocereus
     * Rebutia
     * Rhipsalis
     * Samaipaticereus
     * Schlumbergera
     * Sclerocactus
     * Selenicereus
     * Stenocactus
     * Stenocereus
     * Stephanocereus
     * Stetsonia
     * Strombocactus
     * Tacinga
     * Tephrocactus
     * Thelocactus
     * Tunilla
     * Turbinicarpus
     * Uebelmannia
     * Weberbauerocereus
     * Weberocereus
     * Yungasocereus

Cacti in culture

   In Israel, the cactus is a symbol of Israeli-born Jews, called sabras
   ("prickly pear"), as opposed to those immigrated to it (the latter
   usually include the parents or grandparents of the former), even though
   the cactus itself is not a native plant. The cactus is supposed to
   resemble the character of those as "rough from the outside but soft and
   sweet from the inside". .

   One of the first Israeli children TV shows, Ma Pit'om, had a puppet of
   a cactus named Kishkashta as its main character and as one of the
   show's hosts .
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