APG classification
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The Angiosperm Phylogeny Group (APG) is an international group of botanists who developed a modern, molecular-evidence based classification system for flowering plants known as the APG system. The APG system was first published in 1998 and is updated periodically, with the current version being APG IV from 2016. It is based on analysis of chloroplast and ribosomal DNA sequences. The APG system aims to make taxonomic groups monophyletic based on phylogenetic relationships, retains the Linnaean hierarchy of orders and families, and takes a broad approach in defining taxonomic limits. It recognizes 59 orders and 415 families within the angiosperms.
APG classification
- 1. APG (Angiosperm Phylogeny Group) III classification Ashutosh Mukherjee Department of Botany, Vivekananda College, 269, Diamond Harbour Road, Thakurpukur, Kolkata - 700063, West Bengal, India. The Angiosperm Phylogeny Group, or APG, refers to an informal international group of systematic botanists who came together to try to establish a consensus view of the taxonomy of flowering plants (angiosperms). APG (Angiosperm Phylogeny Group) system is a modern, mostly molecular evidence based phylogeny of flowering plants. The first APG classification was published in 1998 followed by APG II in 2003, APG III in 2009 and APG IV in 2016. APG classification was based on two chloroplast and one ribosomal genes. The overall principles of the APG's approach to classification are: 1. The Linnean system of orders and families should be retained. "The family is central in flowering plant systematics." An ordinal classification of families is proposed as a "reference tool of broad utility". Orders are considered to be of particular value in teaching and in studying family relationships. 2. Groups should be monophyletic (i.e. consist of all descendants of a common ancestor). The main reason why existing systems are rejected is because they do not have this property, they are mostly not phylogenetic. 3. A broad approach is taken for defining the limits of groups. Thus of orders, it is said that a limited number of larger orders will be more useful. Families containing only a single genus and orders containing only a single family are avoided where this is possible without violating the over-riding requirement for monophyly. Structure of APG III system As APG is based on cladistic approach, it does not always refer formal groups. However, it includes 59 orders and 415 families. The higher order classification divided the whole angiosperms into different clades like the following:
- 2. Clade angiosperms (4 orders; eg: Amborellales, Nymphaeales) Clade magnoliids (4 orders; eg: Magnoliales, Piperales) Clade monocots (7 orders; eg: Acorales, Alismatales, Asparagales) Clade commelinids (4 orders: Arecales, Commelinales, Poales and Zingiberales; 1 family) Probable sister of Eudicots (order Ceratophyllales) Clade eudicots (4 orders; eg: Ranunculales; 1 family unplaced in an order) Clade Core Eudicots (2 orders; eg: Saxifragales; 1 family unplaced in an order) Clade Rosids (Order Vitales) Clade Fabids (8 orders; eg: Cucurbitales, Fabales) Clade Malvids (8 orders; eg: Brassicales; Malvales) Clade Asterids (orders Cornales and Ericales) Clade Lamiids (5 unplaced families and 4 orders; eg: Lamiales, Solanales) Clade Campanulids (7 orders; eg: Apiales, Asterales) Merits 1. It adopts the phylogenetic principle of monophyly. 2. It has derived information from sources like morphology, embryology, molecular biology, anatomy, palynology and phytochemistry. 3. Formal names are given only where monophyly has been firmly established. 4. It is based on the recent advances in research and is gaining authority. Demerits 1. It is limited to the taxonomic level of order and family. 2. It is not very popular. 3. Several families or genera have not been placed yet. 4. The orders are recognized under informal groups like Magnoliids, Eudicots. These names do not conform to the ICN.