Kaktuspflanze

Cactus, (Familie Cactaceae), Plural Kakteen oder cactuses, Pflanzefamilie (um Caryophyllales) mit fast 2000 Arten und 139 Gattungen. Kakteen sind auf dem größten Teil Nord- und Südamerikas beheimatet, von British Columbia und Alberta nach Süden. Die südlichste Grenze ihres Verbreitungsgebiets erstreckt sich weit nach Chile und Argentinien. Mexiko hat die größte Anzahl und Artenvielfalt. Die einzigen möglicherweise in der Alten Welt heimischen Kakteen sind Mitglieder der Gattung Rhipsalis, die in Ostafrika, Madagaskar und Sri Lanka vorkommen. Obwohl einige Kaktusarten in tropischen oder subtropischen Gebieten leben, leben die meisten in trockenen Regionen und sind gut an diese angepasst. Siehe auch Liste der Pflanzen der Familie der Cactaceae.

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Caryophyllales: Cactaceae

Die Kakteen sind neugierige, oft dornige (stachelige) Pflanzen mit saftigem Stiel, die die Familie der Kakteen bilden, charakteristisch für und gut angepasst

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Physikalische Eigenschaften

Kakteen sind saftige mehrjährige Pflanzen. Kakteen haben im Allgemeinen dicke krautige oder holzige Chlorophyll-haltige Stängel. Kakteen unterscheiden sich von anderen Sukkulenten durch das Vorhandensein von Areolen, kleinen kissenartigen Strukturen mit Trichomen (Pflanzenhaaren) und bei fast allen Arten von Stacheln oder Stachelborsten (Glochiden). Areolen sind modifizierte Zweige, aus denen Blüten, mehr Zweige und Blätter (falls vorhanden) wachsen können.

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In most species, leaves are absent, greatly reduced, or modified as spines, minimizing the amount of surface area from which water can be lost, and the stem has taken over the photosynthetic functions of the plant. Only the tropical genera Pereskia and Pereskopsis, both vines, have conventional-looking functional leaves, while the leaves of the Andean Maihuenia are rounded, not flattened. The root systems are generally thin, fibrous, and shallow, ranging widely to absorb superficial moisture.

Cacti vary greatly in size and general appearance, from buttonlike peyote (Lophophora) and low clumps of prickly pear (Opuntia) and hedgehog cactus (Echinocereus) to the upright columns of barrel cacti (Ferocactus and Echinocactus) and the imposing saguaro (Carnegiea gigantea). Most cacti grow in the ground, but several tropical species—including leaf cactus (Epiphyllum), Rhipsalis, and Schlumbergera—are epiphytes, growing on other plants; others live on hard substrates such as rocks, while yet others climb far up trees. Epiphytic species tend to have thin, almost leaflike flattened stems. The appearance of the plant varies also according to whether the stem surface is smooth or ornamented with protruding tubercles, ridges, or grooves.

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The primary method of reproduction is by seeds. Flowers, often large and colourful, are usually solitary. All genera have a floral tube, often with many petal-like structures, and other less colourful and almost leaflike structures; the tube grows above a one-chambered ovary. A style topped by many pollen-receptive stigmas also arises from the top of the ovary. The fruit is usually a berry and contains many seeds. Soon after pollination, which may be effected by wind, birds, insects, or bats, the entire floral tube detaches from the top of the ovary to leave a prominent scar.

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Several cacti develop plantlets at ground level that, as offsets, reproduce the species vegetatively. Many others can reproduce by fragmentation, whereby segments broken from the main plant will readily root to form clonal individuals. Tissues of cacti are broadly compatible so that terminal portions of one species may be grafted on top of another.

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The internal structure of cacti stems conforms to the pattern of broad-leaved angiosperms; a cambium layer of dividing cells, located between the woody inner tissues and those near the outside of the stem, is present. The bulk of the stem, however, consists of thin-walled storage cells that contain mucilaginous substances that prevent the loss of moisture. The stem of cacti is the main food-manufacturing and food-storage organ for most species.

Uses

Cacti are widely cultivated as ornamentals. In addition, various species, notably prickly pears and chollas (Opuntia and Cylindopuntia, respectively), are cultivated as food. In Central and South America, species of Opuntia, Cereus, and others are used as living fences, and wood from columnar cacti is used as fuel in some desert regions. In times of drought, the spines are removed from cacti such as mandacaru (Cereus jamacaru) to use as fodder for livestock. Peyote, from Lophophora williamsii, has been used ceremonially since pre-Columbian times for its hallucinogenic properties, and many cactus species are of local importance in traditional medicine.