Plant taxonomy is the science that finds, identifies, describes, classifies, and namesplants. It is one of the main branches oftaxonomy—the science that finds, describes, classifies, and names living organisms.
Plant taxonomy is closely allied toplant systematics, and there is no sharp boundary between the two. In practice, "plant systematics" involves relationships between plants and theirevolution, especially at the higher levels, whereas "plant taxonomy" deals with the actual handling of plantspecimens. The precise relationship between taxonomy and systematics, however, has changed along with the goals and methods employed.
Plant taxonomy is well known for being turbulent, and traditionally not having any close agreement oncircumscription and placement oftaxa. See thelist of systems of plant taxonomy.
Classification systems serve the purpose of grouping organisms by characteristics common to each group. Plants are distinguished from animals by various traits: they havecell walls made ofcellulose,polyploidy, and they exhibit sedentary growth. Where animals have to eat organic molecules, plants are able to change energy from light into organic energy by the process ofphotosynthesis. The basic unit of classification isspecies, a group able to breed amongst themselves and bearing mutual resemblance, a broader classification is thegenus. Several genera make up a family, and several families an order.[1]
The botanical termangiosperm, or flowering plant, comes from theGreekangeíon (ἀγγεῖον; 'bottle, vessel') andspérma (σπέρμα; 'seed'); in 1690, the termAngiospermae was coined byPaul Hermann, albeit in reference to only a small subset of the species that are known as angiosperms, today. Hermann's Angiospermae included only flowering plants possessing seeds enclosed in capsules, distinguished from hisGymnospermae, which were flowering plants withachenial or schizo-carpic fruits (the whole fruit, or each of its pieces, being here regarded as a seed and naked). The terms Angiospermae and Gymnospermae were used byCarl Linnaeus in the same sense, albeit with restricted application, in the names of the orders of his class Didynamia.[2]
The terms angiosperms and gymnosperm fundamentally changed meaning in 1827, whenRobert Brown determined the existence of truly-naked ovules in theCycadeae andConiferae.[3] The termgymnosperm was, from then-on, applied to seed plants with naked ovules, and the termangiosperm to seed plants with enclosed ovules. However, for many years after Brown's discovery, the primary division of the seed plants was seen as between monocots and dicots, with gymnosperms as a small subset of the dicots.[4]
In 1851,Hofmeister discovered the changes occurring in the embryo-sac of flowering plants, and determined the correct relationships of these to theCryptogamia. This fixed the position of Gymnosperms as a class distinct from Dicotyledons, and the term Angiosperm then, gradually, came to be accepted as the suitable designation for the whole of the flowering plants (other than Gymnosperms), including the classes of Dicotyledons and Monocotyledons.[4] This is the sense in which the term is used, today.[5]
In most taxonomies, the flowering plants are treated as a coherent group; the most popular descriptive name has been Angiospermae, withAnthophyta (lit. 'flower-plants') a second choice (both unranked). TheWettstein system andEngler system treated them as a subdivision (Angiospermae). TheReveal system also treated them as a subdivision (Magnoliophytina),[6] but later split it to Magnoliopsida, Liliopsida, and Rosopsida. TheTakhtajan system andCronquist system treat them as a division (Magnoliophyta).[citation needed] TheDahlgren system andThorne system (1992) treat them as a class (Magnoliopsida). TheAPG system of 1998, and the later 2003[7] and 2009[8] revisions, treat the flowering plants as an unranked clade without a formal Latin name (angiosperms). A formal classification was published alongside the 2009 revision in which the flowering plants rank as a subclass (Magnoliidae).[9]
The internal classification of this group has undergone considerable revision. TheCronquist system, proposed byArthur Cronquist in 1968 and published in its full form in 1981, is still widely used but is no longer believed to accurately reflectphylogeny. A consensus about how the flowering plants should be arranged has recently begun to emerge through the work of theAngiosperm Phylogeny Group (APG), which published an influential reclassification of the angiosperms in 1998. Updates incorporating more recent research were published as theAPG II system in 2003,[7] theAPG III system in 2009,[8][10] and theAPG IV system in 2016.
Traditionally, the flowering plants are divided into two groups,
to which the Cronquist system ascribes the classes Magnoliopsida (from "Magnoliaceae") and Liliopsida (from "Liliaceae"). Other descriptive names allowed by Article 16 of theICBN include Dicotyledones or Dicotyledoneae, and Monocotyledones or Monocotyledoneae, which have a long history of use. In plain English, their members may be called "dicotyledons" ("dicots") and "monocotyledons" ("monocots"). The Latin behind these names refers the observation that the dicots most often have twocotyledons, or embryonic leaves, within each seed. The monocots usually have only one, but the rule is not absolute either way. From a broad diagnostic point of view, the number of cotyledons is neither a particularly handy, nor a reliable character.[citation needed]
Recent studies, as per the APG, show that the monocots form amonophyletic group (aclade), but that the dicots areparaphyletic; nevertheless, the majority of dicot species fall into a clade with theeudicots (or tricolpates), with most of the remaining going into another major clade with themagnoliids (containing about 9,000 species). The remainder includes a paraphyletic grouping of early-branching taxa known collectively as thebasal angiosperms, plus the familiesCeratophyllaceae andChloranthaceae.[citation needed]
The plant kingdom is traditionally divided according to the following:
| Latin | Common | No. of species | Notes |
|---|---|---|---|
| Bryophyta | Mosses | approx. 25,000 | No vascular system, distinctive vegetative structures,spores produced for reproduction require damp conditions for survival, many of them are important to the early stages ofsoil formation. |
| Pteridophyta | Ferns | approx. 13,000 | Identifiable root, leaf and stem systems but still produce spores instead of seed. |
| Gymnosperms | Non-flowering seed plant | approx. 1,000 | They are a group of seed producing plants, which includeConiferophyta,Ginkgophyta,Cycadophyta andGnetophyta. |
| Angiosperms | Flowering plants | approx. 300,000 | They are divided into two main classes themonocotyledons anddicotyledons, produce seeds that are protected by fruits. |
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Three goals of plant taxonomy are the identification, classification and description of plants. The distinction between these three goals is important and often overlooked.
Plant identification is a determination of the identity of an unknown plant by comparison with previously collected specimens or with the aid of books or identification manuals.[11] The process of identification connects the specimen with a published name. Once a plant specimen has been identified, its name and properties are known.
Plant classification is the placing of known plants into groups or categories to show some relationship.Scientific classification follows a system of rules that standardizes the results, and groups successive categories into ahierarchy. For example, thefamily to which thelilies belong is classified as follows:[12]
The classification of plants results in an organized system for the naming and cataloging of future specimens, and ideally reflects scientific ideas about inter-relationships between plants. The set of rules and recommendations for formal botanical nomenclature, including plants, is governed by theInternational Code of Nomenclature for algae, fungi, and plants abbreviated as ICN.[13]
Plant description is a formal description of a newly discoveredspecies, and takes place only after significant scientific work to determine that a species is in fact new to science. New descriptions are usually published in the form of ascientific paper using ICN guidelines.[14] The names of these plants can then be registered to theInternational Plant Names Index along with other validly published names.[15]
These include;
SeeCategory: Online botany databases
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This article incorporates text from a publication now in thepublic domain: Chisholm, Hugh, ed. (1911). "Angiosperms".Encyclopædia Britannica (11th ed.). Cambridge University Press.| Subdisciplines | |||||||||||
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