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Cactaceae (The Cactus Family)

Dictionary of botanic terminology - index of names

 Domain: Eukarya (Eukaryotes)
     Kingdom:  Plantae (Plants)
          Subkingdom:
  Tracheophyta (Vascular Plants)
               Superdivision:
  Spermatophyta (Seed Plants)
                    Subdivision:
  Magnoliophytina (Angiosperms)
                        Division (phylum):
  Magnoliophyta (Flowering Plants)
                            Class:
  Magnoliopsida (Dicotyledons)
                                Subclass:
 Caryophyllidae                                                                    
                                    Order:
Caryophyllales                                                                      
                                        Family:
Cactaceae  


Generally the the family is divided into three subfamilies (treated previously as tribes) : Pereskioideae, Opuntioideae, and Cactoideae. Recently a fourth group has been added, the subfamily, Maihuenioideae.

Diversity:  As for many flowering plant the opinions of taxonomist vary (Lumpers vs. splitters) with regard to the number of genera and species, some accept only about 30 genera and 1000 species, while other suggest the number of genera is closer to 200 with over than 2000 species. But the tendency is to consider valid about 90-100 genera and about 2000 species.

Distribution: Endemic of the Americas,  with natural geographic limits from just south of the Arctic Circle in Canada to the tip of Patagonia in South America, and virtually every habitat in-between, mostly in xeric areas. (With only one exception, a few epiphytic species of the pencil cactus (Rhipsalis,) that are found in Africa, Madagascar and  Ceylon) Cacti grow at altitudes from below sea level (e.g., at Death Valley, CA) to over 4,800 m in the Andes; Naturalized in Australia, South Africa, the Mediterranean etc. They live in climates having no measurable rainfall to more than 500 cm of annual precipitation, those of arid regions are typically spiny whereas those from moist, tropical regions tend to be spineless as well as epiphytic.

cactusHabit :  The Cactaceae Perennials herbs (no secondary xylem), with reticulate, lignified vascular systems that provide a supportive frame.  Mainly stem succulents, shrubs and trees with photosynthetic stems. Cacti vary in size from miniature plant of a few cm to as tall as 20+ m and weighing several tons.Solitary to forming mats or clumps, terrestrial (sometimes deep-seated in substrate), self supporting, or epiphytic, or climbing. Typically with spines in association with condensed hairy axillary buds (areoles) and  podaria (tubercles). Usually with ‘cactoid’ appearance or with cylindrical-ridged stems ('cereoid') or with cladodes.

Leaves:  The leaves usually are not present, if present they are generally ephemeral and extremely reduced alternate, spirally arranged, simple, entire and without stipule and quickly fall off, only a few of the more ancestral species (e.g. Pereskia) still produce broad well developed and fleshy lamina. Leaves arise from areoles .

Spines: Cactus spines are modified leaf lacking vascular tissue that arise multiply from the areoles and detach easily. They are classified into central spines located centrally on the areole and radial spines around the margins, they can be stout and woody or fine and hair-like, woolly, bristly, needle-like, barbed, hooked or curved and variously coloured. . They protect the fat stem against some predators, even if inefficiently, but their most important function is to condense atmospheric moisture from dews, fog and rain (spines operate as a drip tip) so that they drip to the ground near the base of the plant for uptake by the superficial root system. Often spines protect plants from the sun and from extreme temperatures helping to preserve the plants from drying out. They also consent to camouflage the plant (mimesis).

FlowersCactus Flowers  medium-sized to large (often showy); flower tube 0.2-15[-30] cm; 1(-several) per areole; arising from axil of tubercle in the youngest areoles at the apex of the plant, or in the older areoles away from the apex, then often forming a ring around the apex; sessile (Pedicellate in Pereskia); fragrant, or odourless; nocturnal or diurnal; bisexual  perfect (rarely unisexual); Actinomorfic (usually) to somewhat zygomorphic; partially acyclic. In cactus the flowers and the true ovary  is hidden in the tips of specialized long shoots which strongly resemble inferior ovaries but often with areoles, scales, bracts and spines (or glochids in Opuntia) persistent or deciduous  The fused stem ripens with the true ovary to become fruit wall.
Floral formula:

 

Ca   Co∞  A

G


Longitudinal section of a flower of Opuntia

Perianth:  Weakly differentiated perianth segments [tepals] sequentially intergrading from outer bractlike sepaloids to inner petaloid; (5–100 ‘many’); free, or joined (basally) from an epigynous zone all connate basally to form a tubular hypanthium. Green, white, cream, yellow, orange, red, pink or purple. Deciduous or persistent on fruit.

Androecium:  typically consists of a very large number of stamens (30-1500+) arising from the inner face of the epigynous zone [hypanthium]

Gynoecium: Consists of a compound pistil of (3-20 ‘many’) carpels, an equal number of stigmas, and an equal number of parietal placentae; ovary apparent inferior (perigynous and superior in Pereskia) sunken into stem tissue with tubercles and areoles present or absent, unilocular with many ovules and placentation mostly parietal; style 1, long, solitary terminated by numerous, spreading wet, lobed stigmas

 

  • Inflorescence:  flowers solitary  and emerging from areoles or bursting through epidermis or at the branch tips (arranged in true inflorescence only in subfamily. Pereskioideae in cymes or panicles or chains of fruits proliferating from fruit areoles (in Cylindropuntia fulgida)
Reproductive type:  Plants hermaphrodite (usually), self-sterile (usually).

Pollination:  Anemophilous, or entomophilous (meliottophilus, sphingophilous), or ornithophilous, or cheiropterophilous.

Fruit: The fruit is a one-celled False berry (generally pulpy ) or rarely a dry capsule, indehiscent or seldom dehiscent, often with scales, areoles, spines or bristles.

seed:

Seedling: Germination phanerocotylar.

Physiology, biochemistry: Presence of betalains pigment, Cyanogenic (rarely), or not cyanogenic. Alkaloids present (usually), or absent. Iridoids not detected. Proanthocyanidins absent. Flavonols present, or absent; quercetin, or kaempferol and quercetin. Ellagic acid absent (3 genera). Saponins/sapogenins present, or absent. CAM (nearly always), or C3 (dubiously?).


Cytology : Chromosomes basic number  X = 11 

Particular characteristic: p-plastids.

Fossil Evidence: No known fossil record. Cacti derives from unknown ancestor (Portulacaceae?) probably somewhere in West Gondwana, probably in South America,  perhaps in the early Cretaceous 90-100 million years ago. But at present we don’t known any convincing fossil that support this hypothesis. Fossilization usually need sedimentation of mineral materials over vegetative materials, and unfortunately this is a very rare combination for plant growing in xeric areas .

The origin of all cacti is probably in South America,



Cactus relatives: The Cactaceae were once classified near the carrot family (Apiaceae), but now the family is placed in a very different order, the Caryophyllales, along with the only other betalain-producing angiosperm families, Achatocarpaceae, Aizoaceae, Amaranthaceae, Basellaceae, Chenopodiaceae, Didieriaceae, Nyctaginaceae, Phytolaccaceae, and Portulacaceae. Recent studies of DNA variation and from vascular anatomy, revealed that the closest angiosperm family to the cacti is the Portulacaceae. The aged and well established assumptions that the Aizoaceae (including the mesembs) was the sister family to the cacti (due to the floral hypanthium) was proved fallacious in independent tests of phylogeny for the order
Caryophyllales.


Economic Uses: Highly appreciated as ornamentals, many in the wild are on verge of extinction because unscrupulous collectors have dug them. Edible fruits (prickly pear, India fig, tuna, arridari, pitaya), noxious weeds in some places where introduced (Australia, Hawaii...)

 
 
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