Introduction
The classification of the family Cactaceae remains uncertain as of March 2012. Since the mid-1990s, the system produced by the International Cactaceae Systematics Group (ICSG) of the International Organization for Succulent Plant Study has been used as the basis of many published classifications. Detailed treatments produced 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.
The ICSG classification of the family recognizes four subfamilies: Pereskoideae (consisting only of the genus Pereskia), Opuntioideae, Maihuenioideae (consisting only of the genus Maihuenia) and Cactoideae. Molecular phylogenetic studies suggest that Pereskia is not monophyletic (i.e. its species are not the complete set of descendants of a common ancestor), although the three other subfamilies are. The Bayesian consensus cladogram from a 2005 study is shown below:
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Pereskioideae |
Five tribes have been recognized within the subfamily Opuntioideae: Tephrocacteae, Pterocacteae, Austrocylindropuntieae, Cylindropuntieae and Opuntieae. All but the first, Tephrocacteae, were shown to be "essentially monophyletic" in molecular phylogenetic study in 2009. A summary of the consensus Bayesian tree is shown below (tribes are bold; the number of species in the study is shown in parentheses).
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≈ Opuntieae |
Many of the genera within the Opuntioideae are not monophyletic. Maihueniopsis is highly polyphyletic, appearing in four separate lineages. The two largest genera within the subfamily, Opuntia and Cylindropuntia are also not monophyletic. The classification of the Opuntioideae is thus uncertain as of March 2012; Griffith and Porter say that changes in classification will require "broad information (of multiple data types) regarding all species of opuntioid cacti".
The ICSG classification divides the subfamily Cactoideae into nine tribes. However, phylogenetic research has not supported most of these tribes, nor even the genera of which they are composed. A 2011 study found that "an extraordinarily high proportion of genera" were not monophyletic, including 22 (61%) of the 36 genera in the subfamily Cactoideae sampled in the research. Of the nine tribes recognized within Cactoideae, one, Calymmantheae, comprises a single genus, Calymmanthium. Of the remaining eight, only two (Cacteae and Rhipsalideae) have been shown to be monophyletic. A summary of the cladograms for the Cactoideae presented in a 2011 paper is shown below (ICSG tribes in bold).
| Cactoideae |
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The classification of genera and tribes in the Cactaceae is thus likely to change in future.
Read more about this topic: Classification Of The Cactaceae
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