Editing Botany (section)

== Systematic botany ==
{{Further|Taxonomy (biology)}}
[[File:HerbPrepLG.jpg|thumb|upright=1.25|left|alt=photograph of a botanist preparing plant specimens for the herbarium|A botanist preparing a plant specimen for mounting in the [[herbarium]]]]

Systematic botany is part of systematic biology, which is concerned with the range and diversity of organisms and their relationships, particularly as determined by their evolutionary history.{{sfn|Lilburn|Harrison|Cole|Garrity|2006}} It involves, or is related to, biological classification, scientific taxonomy and [[phylogenetics]]. Biological classification is the method by which botanists group organisms into categories such as [[genus|genera]] or [[species]]. Biological classification is a form of [[Taxonomy (biology)|scientific taxonomy]]. Modern taxonomy is rooted in the work of [[Carl Linnaeus]], who grouped species according to shared physical characteristics. These groupings have since been revised to align better with the [[Charles Darwin|Darwinian]] principle of [[common descent]] – grouping organisms by ancestry rather than [[phenotype|superficial characteristics]]. While scientists do not always agree on how to classify organisms, [[molecular phylogenetics]], which uses [[DNA sequences]] as data, has driven many recent revisions along evolutionary lines and is likely to continue to do so. The dominant classification system is called [[Linnaean taxonomy]]. It includes ranks and [[binomial nomenclature]]. The nomenclature of botanical organisms is codified in the [[International Code of Nomenclature for algae, fungi, and plants]] (ICN) and administered by the [[International Botanical Congress]].{{sfn|McNeill|Barrie|Buck|Demoulin|2011|p = Preamble, para. 7}}{{sfn|Mauseth|2003|pp = 528–551}}

Kingdom [[Plant]]ae belongs to [[Domain (biology)|Domain]] [[Eukaryota]] and is broken down recursively until each species is separately classified. The order is: [[Kingdom (biology)|Kingdom]]; [[Phylum]] (or Division); [[Class (biology)|Class]]; [[Order (biology)|Order]]; [[Family (biology)|Family]]; [[Genus]] (plural ''genera''); [[Species]]. The scientific name of a plant represents its genus and its species within the genus, resulting in a single worldwide name for each organism.{{sfn|Mauseth|2003|pp = 528–551}} For example, the tiger lily is ''[[Lilium columbianum]]''. ''Lilium'' is the genus, and ''columbianum'' the [[Botanical name#Binary name|specific epithet]]. The combination is the name of the species. When writing the scientific name of an organism, it is proper to capitalise the first letter in the genus and put all of the specific epithet in lowercase. Additionally, the entire term is ordinarily italicised (or underlined when italics are not available).{{sfn|Mauseth|2003|pp = 528–555}}{{sfn|International Association for Plant Taxonomy|2006}}{{sfn|Silyn-Roberts|2000|p = 198}}

The evolutionary relationships and heredity of a group of organisms is called its [[Phylogenetics|phylogeny]]. Phylogenetic studies attempt to discover phylogenies. The basic approach is to use similarities based on shared inheritance to determine relationships.{{sfn|Mauseth|2012|pp = 438–444}} As an example, species of ''[[Pereskia]]'' are trees or bushes with prominent leaves. They do not obviously resemble a typical leafless [[cactus]] such as an ''[[Echinocactus]]''. However, both ''Pereskia'' and ''Echinocactus'' have spines produced from [[areoles]] (highly specialised pad-like structures) suggesting that the two genera are indeed related.{{sfn|Mauseth|2012|pp = 446–449}}{{sfn|Anderson|2001|pp = 26–27}}

{{Multiple image|float=right
|title=Two cacti of very different appearance
|total_width=400
|width1=3872|height1=2592|image1=Pereskia aculeata5.jpg|caption1=''Pereskia aculeata''
|width2=4288|height2=3216|image2=Bogarub-echinocactus-grusonii-1.jpg|caption2=''Echinocactus grusonii''
|footer=Although ''Pereskia'' is a tree with leaves, it has spines and areoles like a more typical cactus, such as ''Echinocactus''.}}
Judging relationships based on shared characters requires care, since plants may resemble one another through [[convergent evolution]] in which characters have arisen independently. Some [[euphorbia]]s have leafless, rounded bodies adapted to water conservation similar to those of globular cacti, but characters such as the structure of their flowers make it clear that the two groups are not closely related. The [[Cladistics|cladistic method]] takes a systematic approach to characters, distinguishing between those that carry no information about shared evolutionary history – such as those evolved separately in different groups ([[homoplasies]]) or those left over from ancestors ([[plesiomorphies]]) – and derived characters, which have been passed down from innovations in a shared ancestor ([[apomorphies]]). Only derived characters, such as the spine-producing areoles of cacti, provide evidence for descent from a common ancestor. The results of cladistic analyses are expressed as [[cladogram]]s: tree-like diagrams showing the pattern of evolutionary branching and descent.{{sfn|Mauseth|2012|pp = 442–450}}

From the 1990s onwards, the predominant approach to constructing phylogenies for living plants has been [[molecular phylogenetics]], which uses molecular characters, particularly [[DNA]] sequences, rather than morphological characters like the presence or absence of spines and areoles. The difference is that the genetic code itself is used to decide evolutionary relationships, instead of being used indirectly via the characters it gives rise to. [[Clive A. Stace|Clive Stace]] describes this as having "direct access to the genetic basis of evolution."{{sfn|Stace|2010a|p = 104}} As a simple example, prior to the use of genetic evidence, fungi were thought either to be plants or to be more closely related to plants than animals. Genetic evidence suggests that the true evolutionary relationship of multicelled organisms is as shown in the cladogram below – fungi are more closely related to animals than to plants.{{sfn|Mauseth|2012|p = 453}}

<div style="float: left; margin-right: 15px; ">{{clade
|1={{clade
   |1='''plants'''
   |2={{clade
      |1='''fungi'''
      |2='''animals'''
      }}
   }}
}}
</div>

In 1998, the [[Angiosperm Phylogeny Group]] published a [[phylogenetics|phylogeny]] for flowering plants based on an analysis of DNA sequences from most families of flowering plants. As a result of this work, many questions, such as which families represent the earliest branches of [[angiosperms]], have now been answered.{{sfn|Burger|2013}} Investigating how plant species are related to each other allows botanists to better understand the process of evolution in plants.{{sfn|Chase et al.|2003|pp = 399–436}} Despite the study of model plants and increasing use of DNA evidence, there is ongoing work and discussion among taxonomists about how best to classify plants into various [[Taxon|taxa]].{{sfn|Capon|2005|p = 223}} Technological developments such as computers and [[electron microscope]]s have greatly increased the level of detail studied and speed at which data can be analysed.{{sfn|Morton|1981|pp = 459–459}}

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