Angiosperm Phylogeny Group I (APG I)PABASARA GUNAWARDANE

Angiosperms•The botanical term "Angiosperm", from the Ancient Greek•The flowering plants•Also known as Magnoliophyta•The most diverse group of land plants•Seed-producing plants•Flowers, endosperm within the seeds, and the production of fruits that contain the seed are the distinguished features

Flowering plants diversified and widespread

120 million years

ago

History of Angiosperm Classification•Artificial System:  On the basis of one or few characters of plants•Natural system: A large number of morphological characters were taken into consideration, in the natural systems of classification•Phylogenetic system: Based on evolutionary sequence as well as genetic relationships among different groups of plants

Angiosperm Classification•In the past, classification systems were typically produced by an individual botanist or by a small group•The result was a large number of systems • Different systems and their updates were generally favored in different countries

Bentham & Hooker System

Engler System

Adolf Engler (1844–1930)

Takhtajan System

Armen Takhtajan

Cronquist System

Arthur Cronquist

•Before the availability of genetic evidences, angiosperms were classified using their morphology and biochemistry

•After the 1980’s genetic evidences were available and phylogenetic methods came into action

Angiosperm Phylogeny Group•In the late 1990s, an informal group of researchers from major institutions worldwide came together•Established APG•Objective was to provide a widely accepted and more stable point of reference for angiosperm classification•APG I was published in 1998 as their first attempt in Annals of the Missouri Botanical Garden

Angiosperm Phylogeny Group•The initial 1998 paper by the APG made angiosperms the first large group of organisms to be systematically re-classified primarily on the basis of genetic characteristics•Emphasized the need for a classification system for angiosperms at the level of families, orders and above• Existed systems are rejected is because they are not phylogenetic

Angiosperm Phylogeny Group•The group published 462 families of angiosperms grouped into 40 monophyletic orders

Monophyletic: Consists of an ancestral species and all its descendants

•The outline of a phylogenetic tree of all flowering plants became established•Several well supported major clades* involving many families of flowering plants were identified•the new knowledge of phylogeny revealed relationships in conflict with the then widely used modern classifications• It became clear that none of the previous classifications accurately reflected phylogenetic relationships of flowering plants

 * A clade is a group of organisms that consists of a common ancestor and all its lineal descendants

Principles of the APG system•The Linnean system of orders and families should be retained•Groups should be monophyletic (Consist of all descendants of a common ancestor)•A broad approach is taken to defining the limits of groups such as orders and families•Above or parallel to the level of orders and families, the term clades is used more freely

Features of APG•Formal, scientific names are not used above the level of order, named clades being used instead•A substantial number of taxa whose classification had traditionally been uncertain are given places•Alternative classifications are provided for some groups•A major outcome of the classification is the disappearance of the traditional division of the flowering plants into two groups, monocots and dicots (The monocots are recognized as a clade, but the dicots are not)

Why Dicots became Eudicots??• The angiospermous plants were divided into two distinct classes: the monocotyledons or Monocotyledoneae, and the dicotyledons or Dicotyledoneae• The two cotyledons descriptive of the traditional classification ‘dicots’ also occur in the Coniferales, Cycadales, and Gnetales (Judd and Olmstead 2004) and is now thought as an ancestral feature of the flowering plants and not distinct to any group within.

• The genetic approach is more modern, precise and objective• The system is a group-work• Use of monophyletic groups (i.e. groups which consist of all

descendants of a common ancestor) provides a descriptive link between the groups

• A substantial number of taxa whose classification had traditionally been uncertain are given places

Advantages of APG

• Named clades being used instead of Formal, scientific names above the level of order. thus, eudicots and monocots are not given a formal rank

• Taxa which were uncertain to rank were ranked but 25 families are still remain uncertain position

• Alternative classifications are provided for some groups (e.g. the Fumariaceae can either be treated as a separate family or as part of Papaveraceae)

• What came first and what came after is not clearly determined

Disadvantages of APG

• APG II (2003) and APG III (2009) has been introduced and updated APG I

Updating APG

• A significant number of major herbaria, including Kew, are changing the order of their collections in accordance with APG

• The influential World Checklist of Selected Plant Families (also from Kew) is being updated to the APG III system

• In the USA, a recent photographic survey of the plants of the USA and Canada is organized according to the APG II system.

• In the UK, the latest edition of the standard flora of the British Isles is based on the APG III system

Influence of APG

• The Angiosperm Phylogeny Group (1998) An ordinal classification for the family of flowering plants Annals of the Missouri Botanical Garden Vol. 85, No. 4 (1998), pp. 531-553

• Angiosperm Phylogeny Group II (2003), An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG II (PDF), Botanical Journal of the Linnean Society 141: 399–436

• Ben G. Bareja (2012) Monocots, Dicots and Eudicots Distinguished. Available at: http://www.cropsreview.com/monocots.html (Accessed 22 September 2015)

• Michal Yakir (2013) Which Phylogenic systematics should be used. Available at: http://www.michal-yakir.de/cronquist-apg-1.html (Accessed 22 September 2015)

• Ho Dinh Hai (2012) APG Systems of Plant Classification. Available at: http://www.edibleplantsinvietnam.com/apg-systems-of-plant-classification.html (Accessed 22 September 2015)

References