Editing Cactus (section)

==Taxonomy and classification==
{{multiple image
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|image1 = Botany Bay - Cynara cardunculus 1.jpg
|image2 = Melocactus.JPG
|footer = (Above) The spiny heads of the [[cardoon]], possibly once known as "cactus"; <br>(below) A ''[[Melocactus]]'', likely the first genus seen by Europeans
}}
Naming and classifying cacti has been both difficult and controversial since the first cacti were discovered for science. The difficulties began with [[Carl Linnaeus]]. In 1737, he placed the cacti he knew into two genera, ''Cactus'' and ''Pereskia''. However, when he published ''[[Species Plantarum]]'' in 1753—the starting point for modern botanical nomenclature—he relegated them all to one genus, ''Cactus''. The word "cactus" is derived through Latin from the [[Ancient Greek]] {{lang|grc|κάκτος}} (''kaktos''), a name used by [[Theophrastus]] for a spiny plant,<ref name=JohnSmit72/> which may have been the [[cardoon]] (''Cynara cardunculus'').<ref name=SonnPignHamm07/>

Later botanists, such as [[Philip Miller]] in 1754, divided cacti into several genera, which, in 1789, [[Antoine Laurent de Jussieu]] placed in his newly created family Cactaceae. By the early 20th century, botanists came to feel Linnaeus's name ''Cactus'' had become so confused as to its meaning (was it the genus or the family?) that it should not be used as a genus name. The 1905 Vienna botanical congress rejected the name ''Cactus'' and instead declared ''Mammillaria'' was the type genus of the family Cactaceae. It did, however, [[Conserved name|conserve]] the name Cactaceae, leading to the unusual situation in which the family Cactaceae no longer contains the genus after which it was named.{{sfnp|ps=none|Anderson|2001|p=96}}

The difficulties continued, partly because giving plants scientific names relies on "[[type (biology)|type specimens]]". Ultimately, if botanists want to know whether a particular plant is an example of, say, ''Mammillaria mammillaris'', they should be able to compare it with the type specimen to which this name is permanently attached.  Type specimens are normally prepared by compression and drying, after which they are stored in [[herbarium|herbaria]] to act as definitive references. However, cacti are very difficult to preserve in this way; they have evolved to resist drying and their bodies do not easily compress.{{sfnp|ps=none|Anderson|2001|pp=93–94}} A further difficulty is that many cacti were given names by growers and horticulturalists rather than botanists; as a result, the provisions of the ''[[International Code of Nomenclature for algae, fungi, and plants]]'' (which governs the names of cacti, as well as other plants) were often ignored. [[Curt Backeberg]], in particular, is said to have named or renamed 1,200 species without one of his names ever being attached to a specimen, which, according to [[David Hunt (botanist)|David Hunt]], ensured he "left a trail of nomenclatural chaos that will probably vex cactus taxonomists for centuries."{{sfnp|ps=none|Anderson|2001|p=98}}

===Classification===
{{main article|Taxonomy of the Cactaceae}}
In 1984, it was decided that the Cactaceae Section of the [[International Organization for Succulent Plant Study]] should set up a working party, now called the International Cactaceae Systematics Group (ICSG), to produce consensus classifications down to the level of genera. Their system has been used as the basis of subsequent classifications. Detailed treatments published in the 21st century have divided the family into around 125–130 genera and 1,400–1,500 species, which are then arranged into a number of tribes and subfamilies.{{sfnp|ps=none|Anderson|2001|pp=99–103}}<ref name=Hunt06/><ref name=BarcYessHawk11/> The ICSG classification of the cactus family recognized four subfamilies, the largest of which was divided into nine tribes. The subfamilies were:{{sfnp|ps=none|Anderson|2001|pp=99–103}}
{{multiple image
|title=The four cactus subfamilies
|total_width=320 | perrow = 2
|image1=Pereskia aculeata4 cropped.jpg
|caption1=[[Pereskioideae]]: ''[[Pereskia aculeata]]''
|image2=Opuntia chlorotica 5 cropped.jpg
|caption2=[[Opuntioideae]]: ''[[Opuntia chlorotica]]''

|image3=Maihuenia poeppigii 02 cropped.jpg
|caption3=[[Maihuenioideae]]: ''[[Maihuenia poeppigii]]''
|image4=Warzenkaktus - Mammillaria elongata.JPG
|caption4=Cactoideae: ''[[Mammillaria elongata]]''
}}
* Subfamily Pereskioideae <small>K. Schumann</small>
:The only genus in the ICSG classification was ''Pereskia''. It has features considered closest to the ancestors of the Cactaceae. Plants are trees or shrubs with leaves; their stems are smoothly round in cross section, rather than being ribbed or having tubercles.{{sfnp|ps=none|Anderson|2001|pp=99–103}} Two systems may be used in [[photosynthesis]], both the "normal" [[C3 carbon fixation|C<sub>3</sub> mechanism]] and [[crassulean acid metabolism]] (CAM)—an "advanced" feature of cacti and other [[Succulent plant|succulents]] that conserves water.<ref name=EdwaDono06/>
:[[Molecular phylogenetics|Molecular phylogenetic]] studies showed that when broadly [[Circumscription (taxonomy)|circumscribed]], ''Pereskia'' was not [[monophyly|monophyletic]],<ref name=EdwaNyffDono05/><ref name=BarcYessHawk11/> and it has been split into three genera, ''[[Leuenbergeria]]'', ''[[Rhodocactus]]'' and a narrowly circumscribed ''[[Pereskia]]''.<ref name=Lode13/><ref name=AsaiMiya16/> ''Leuenbergeria'' is then placed on its own in a separate monogeneric subfamily, Leuenbergerioideae.<ref name=MaytMoli15/>
* Subfamily [[Opuntioideae]] <small>K. Schumann</small>
:Some 15 genera are included in this subfamily. They may have leaves when they are young, but these are lost later. Their stems are usually divided into distinct "joints" or "pads" ([[cladode]]s).{{sfnp|ps=none|Anderson|2001|pp=99–103}} Plants vary in size from the small cushions of ''[[Maihueniopsis]]''{{sfnp|ps=none|Anderson|2001|p=399}} to treelike species of ''Opuntia'', rising to {{convert|10|m|ft|abbr=on}} or more.{{sfnp|ps=none|Anderson|2001|p=485}}
* Subfamily [[Maihuenioideae]] <small>P. Fearn</small>
:The only genus is ''Maihuenia'', with two species, both of which form low-growing mats.{{sfnp|ps=none|Anderson|2001|p=398}} It has some features that are primitive within the cacti. Plants have leaves, and crassulean acid metabolism is wholly absent.{{sfnp|ps=none|Anderson|2001|pp=99–103}}
* Subfamily [[Cactoideae]]
:Divided into nine tribes, this is the largest subfamily, including all the "typical" cacti. Members are highly variable in habit, varying from tree-like to [[epiphyte|epiphytic]]. Leaves are normally absent, although sometimes very reduced leaves are produced by young plants. Stems are usually not divided into segments, and are ribbed or tuberculate. Two of the tribes, [[Hylocereeae]] and [[Rhipsalideae]], contain climbing or [[Epiphyte|epiphytic]] forms with a rather different appearance; their stems are flattened and may be divided into segments.{{sfnp|ps=none|Anderson|2001|pp=99–103}}

[[Molecular phylogenetics|Molecular phylogenetic studies]] have supported the [[monophyly]] of three of these subfamilies (not Pereskioideae),<ref name=BarcYessHawk11/><ref name=EdwaNyffDono05/> but have not supported all of the tribes or even genera below this level; indeed, a 2011 study found only 39% of the genera in the subfamily Cactoideae sampled in the research were [[monophyletic]].<ref name=BarcYessHawk11/> Classification of the cacti currently remains uncertain and is likely to change.