Cacti are perennial shrubs , more rarely trees or geophytes . Almost all species are stem succulents , the shoot axes of which are strongly swollen. The roots are usually fibrous or sometimes form succulent tubers or beets in plants with only a low stem succulence . The main rungs, often characteristic of certain genera, are single or branch off from the bases or higher up. Main shoots and branches usually grow upright or ascending, sometimes also creeping or hanging. The rungs are cylindrical or flattened into platycladia and often have well-developed ribs or spirally arranged warts. Areoles , which represent strongly reduced short shoots , are usually distributed on cylindrical or flattened rungs, or otherwise on the ridges of the ribs or warts. They are felty and have thorns that represent transformed leaves, and often wool or bristles. Felt and thorns are always present in young seedlings , but are sometimes shed later or no longer formed by adult plants. The foliage leaves arising from the areoles are sometimes fully developed (subfamily Pereskioideae), often awl-shaped, succulent and short-lived (subfamilies Opuntioideae and Maihuenioideae), but are usually completely absent (subfamily Cactoideae). Stipules are absent.
Cacti can take on very different sizes. Carnegiea gigantea grows up to 15 meters high. The smallest cactus, Blossfeldia liliputana , on the other hand, forms flat spherical bodies barely a centimeter in diameter. The growth rates are also very different. Some cereen grow more than 1 meter per year per shoot. In the case of Aztekium ritteri , on the other hand, there is hardly any noticeable increase even over several years.
The lifespan of the cacti also varies greatly. Slow-growing, large plants such as Carnegiea and species of Ferocactus that can only flower in old age can live up to 200 years. In contrast, the life span of rapidly developing and early flowering plants is shorter. For example, Echinopsis mirabilis , which blooms in its second year of life, is self-fertile and produces abundant seeds, rarely older than 13 to 15 years.
Inside the plants, the vascular bundles are ring-shaped along the central axes, and oval in the case of flattened rungs. Branches of the vascular bundles each lead to an areole. The juice contained is almost always clear; only a few species of Mammillaria contain milk juice .
The flowers usually arise individually, sometimes in small groups, from the areoles, more rarely (in and around Mammillaria ) from the axillae or furrows between the areoles and axillae. Sometimes they are only formed in special, heavily forested or bristle areas ( cephalia ), either along the shoot axes and sunk into them ( Espostoa , Espostoopsis ) or at the end and limiting the growth ( Melocactus , Discocactus ). The flowers are hermaphroditic and mostly radial symmetry , more rarely zygomorphic . The diameters of the flowers vary from 5 mm to 30 cm, but mostly the flowers are relatively large and, in the case of smaller species, often larger than the plant body. The many (five to 50 or more) bracts usually change in shape and structure from the outside to the inside from bract - to corolla-like . Stamens are present in large numbers (50 to 1500, rarely less). Depending on how they adapt to the pollinators ( butterflies , moths , bats , hummingbirds or bees ), the flowers are open at night (often only for a few hours) or during the day (usually for several days) and are tubular, bell-shaped or wheel-shaped. They usually open wide, but sometimes only slightly if they are tubular. Rarely (in Frailea ) the flowers are cleistogamous and only open in exceptional cases. The ovaries are mostly below (in subfamily Pereskioideae half above). The areas of the flower (ovaries) containing the ovaries are usually reinforced with scales, thorns or wool on the outside and separated with hair on the inside.
The berry-like , often fleshy and strikingly colored fruits when ripe contain a few to mostly many (up to about 3000) 0.4 to 12 mm large seeds . Goats , birds , ants , mice and bats contribute significantly to the spread of the seeds. The seeds of most species of cacti are light germs .
The basic chromosome number is x = 11.
With the exception of Rhipsalis baccifera , the natural occurrence of cacti is limited to the American continent . There their distribution area extends from southern Canada to Patagonia in Argentina and Chile . The greatest density of cacti can be found in the areas around the northern ( Mexico ) and southern tropics (Argentina / Bolivia ).
Cacti inhabit a wide variety of habitats, from lowlands to high mountains , from tropical rainforests to steppes and semi-deserts to arid deserts . All habitats have in common that the water necessary for survival is not available all year round, but only seasonally.
The plant family of cacti with around 100 to 130 genera and 1500 to 1800 species is divided into four subfamilies:
contains one genus ( Pereskia ) with around 16 species: non-succulent to weakly succulent plants ( C 3 plants ) without glochids, with fully developed leaves and large, black seeds without a seed coat.
contains about 300 species: Plants with reduced awl-shaped, succulent, but very short-lived leaves, glochids and mostly light-colored seeds with an always rock-hard seed coat.
contains a genus ( Maihuenia ) with only two species: mat-forming plants similar to those of the Opuntioideae, but with longer-lived leaves, black seeds and without glochids.
contains more than 85 percent of the species; almost always completely leafless plants without glochids and with seeds without a seed coat.
Use and protection
As early as the Aztecs , cacti, especially Echinocactus grusonii, were repeatedly found in pictorial representations, sculptures and names . This cactus, also known as the “mother-in-law's chair”, had great ritual significance - human sacrifices were made on it . Tenochtitlán , today's Mexico City , means place of the sacred cactus . The state coat of arms of Mexico still bears an eagle , snake and cactus today . The economic use of cacti also goes back to the Aztecs. The Indians of North America used the content of alkaloids in some cacti for their ritual acts . They made fishhooks from the bent thorns of some cacti .
Nowadays, in addition to being used as food ( jam , fruit , vegetables ) , cacti are primarily used as host plants for the cochineal scale insect , from which red dye for Campari or high-quality lipsticks is obtained. In South America in particular , dead columnar cacti provide valuable timber . Some cacti are also important for pharmacy . Cacti are also grown as house plants.
Cacti enjoyed growing popularity over time, sometimes they were reserved for science , and often they experienced a real boom as fashion plants. Since the beginning of the 20th century, interest in cacti has increased steadily, interrupted only by the two world wars . Associated with this was also the increasing commercial interest, the negative excesses of which culminated in veritable raids on the cactus sites and resulted in the extinction of many species. Due to the large number of cactus lovers, be it as a hobby or out of scientific interest, new species and varieties are still found every year .
With the exception of the genera Pereskia , Pereskiopsis and Quiabentia , all cacti are covered by the Washington Convention on Endangered Species ; many species are completely protected by being included in Appendix I. Some countries take a somewhat contradicting stance on conservation. In Mexico, for example, you can get a prison sentence if you are caught digging up cacti, but on the other hand, cactus sites are being destroyed in favor of new roads and power lines. It is particularly worrying that some cactus locations have an area of no more than 1000 square meters. If this location is destroyed (construction work, looting), the species that grow there is lost to posterity if it is endemic , i.e. only occurs there and nowhere else.
The following German-speaking societies promote the knowledge and care of cacti and other succulents, etc. a. through the exchange of experiences, exhibitions, lectures and the publication of the joint magazine Kakteen und Other Succulents (KuaS).
- Edward Frederick Anderson: The Great Cactus Lexicon . Eugen Ulmer, Stuttgart (Hohenheim) 2005, ISBN 3-8001-4573-1 .
- David Hunt, Nigel Taylor, Graham Charles: The New Cactus Lexicon . dh Books, Milborne Port 2006, ISBN 0-9538134-4-4 .
- Bruce D. Parfitt, Arthur C. Gibson: Cactaceae . In: Flora of North America Volume 4, 2003, p. 92 ( online ; section description).
- L. Watson, MJ Dallwitz: The family of the Cactaceae at DELTA by L. Watson & MJ Dallwitz. (Section description)
- The Cactaceae family on the AP website. (Sections Description and Systematics)
- Park S. Nob: Cacti: Biology and Uses . University of California Press, 2002, ISBN 0-520-23157-0 , p. 82.
- R. Nyffeler, U. Eggli: Disintegrating Portulacaceae: A new familial classification of the suborder Portulacineae (Caryophyllales) based on molecular and morphological data . In: Taxon . Volume 59, Number 1, 2010, pp. 227-240.
- CITES: Appendices I, II and III. September 19, 2012, accessed January 5, 2010 .