APG III Classification

PLANT SYSTEMATICS APG III CLASSIFICATION “BEHOLD HER, SINGLE IN THE FIELD” A PRESENTATION BY DR. N. SANNIGRAHI, ASSOCIATE PROFESSOR DEPARTMENT OF BOTANY, NISTARINI COLLEGE, PURULIA, D.B. ROAD, PURULIA (W.B) INDIA, 723101 PLANT CLASSIFICATION   Until detailed genetic evidence became available, the classification of flowering plants was based on their morphology (particularly that of the flower) and their biochemistry (what kinds of chemical compound they contained or produced). Classification systems were typically produced by an individual botanist or by a small group. The result was a large number of such systems. Different systems and their updates tended to be favored in different countries; e.g. the Engler system in continental Europe; the Bentham & Hooker system in Britain (particularly influential because it was used by Kew); the Takhtajan system in the former Soviet Union and countries within its sphere of influence; and the Cronquist system in the United States. 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) that would reflect new knowledge about their relationships based upon phylogenetic studies. The Taxonomy being synthetic science has been developed from time to time by the addition of value in every respect. PLANT CLASSIFICATION  They set the most recent classification of flowering plants based on phylogenetic data - the Angiosperm Phylogenetic Group classification. Its four versions (APG I, APG II, APG III & APG IV) have been published in 1998, 2003, 2009 and 2016 respectively. Each version supplants the previous version. Recognition of monophyletic group based on the information received from various disciplines such as gross morphology, anatomy, embryology, palynology, karyology, phytochemistry and more strongly on molecular data with respect to DNA sequences of two chloroplast genes (atpB and rbcL) and one nuclear gene (nuclearribosomal 18s DNA). The most recent updated version, APG IV (2016) recognized 64 orders and 416 families. Of these 416 families, 259 are represented in India.  The Plant classification is very dynamic one with the passage of time and more and more data input from the different domains of knowledge has ultimately made the journey more fascinating and colorful. PLANT CLASSIFICATION & APG  In the early 1990s, the first large analyses of flowering plants based on DNA sequences were published. These had become possible due to major developments in DNA sequencing technology and computing power in the late 20th century. Flowering plants were the first major group on which large groups of scientists collaborated in comprehensive analyses of this type, collecting sequences for the same genes, so that the data could be combined. In 1993, a landmark paper with an analysis of 500 flowering plants was published by Mark Chase, and co-authors, the year after Mark moved from the University of North Carolina to Kew along with Brigittia Bremer, Kare Bremer, Walter S. Judd, David J Mabberley, Peter F Stevens. This paper was based on sequences of one of the major genes involved in photosynthesis, and the analysis involved the botanists working with the computer programmers because the program had to be rewritten to allow them to analyze such a large data set. The Original APG system of Plant classification based on cladistics analysis of DNA sequence . PRINCIPLES OF APG SYSTEM i. ii. iii. iv. v. The principles of the APG’s approach to classification were set out in the first paper of 1998 and it has remained unchanged in the subsequent revisions like APGII, APGIII & APGIV. The basic principles are as followed: The Linnaean system of orders and families should be retained.” The family is central in flowering plant systematics”. An ordinal classification of families as proposed as “reference tool of broad utility”. Orders are treated for teaching and studying family relationship. Groups should be monophyletic i.e. all have been derived from common ancestor. The main reason why existing systems are rejected because they do not have the property , they are not phylogenetic. A broad approach is taken to defining the limits of the groups. Large orders are considered more useful. Families with single genus and orders having single family are kept out side. It is made so keeping monophyly in view. Named clades ate used to families and orders. The authors point out that it is not possible or desirable to name all clades in phylogenetic tree; naming some clades particularly orders and families make it easy to exchange views and enhance discussion. APG III CLASSIFICATION  The APGIII system (2009) of plant classification is the third version of its kind mostly based on molecular taxonomy and it was published after 6 and ½ years of APG II plant classification. Members of the Linnaean society put forth a formal phylogenetic classification of all land plants , compatible with the APG III.The system consists of 45 orders on the taxonomic rank and 14 new ones. The newly recognized orders are Amborellales, Nymphaeales, Chloranthales, Petrosaviales, Trochodendrales, Buxales, Vitales, Zygophyllales, Picramniales, Huerteales. Berberidopsidales, Escalloniales, Bruniales and Paracryphiales.  The alternative “Bracket families” were left out in APG III, because its inclusion in the previous system had been unpopular .  APG III recognizes 415 families, 42 fewer than the previous system. $$ of the 55 bracketed families were discontinued and 18 other families were discontinued. APG III CLASSIFICATION  The designation of alternative "bracketed families" was abandoned in APG III, because its inclusion in the previous system had been unpopular. APG III recognized 415 families, 42 fewer than in the previous system. Fortyfour of the 55 "bracketed families" were discontinued, and 18 other families were discontinued as well. The discontinued bracketed families were: Illiciaceae, Alliaceae, Agapanthaceae, Agavaceae, Aphyllanthaceae, Hesperocallidaceae, Hyacinthaceae, Laxmanniaceae, Ruscaceae, Themidaceae, Asphodelaceae, Hemerocallidaceae, Kingdoniaceae, Fumariaceae, Pteridophyllaceae, Didymelaceae, Tetracentraceae, Pterostemonaceae, Hypseocharitaceae, Francoaceae, Memecylaceae, Lepuropetalaceae, Rhoipteleaceae, Medusagynaceae, Quiinaceae, Malesherbiaceae, Turneraceae, Bretschneideraceae, Diegodendraceae, Cochlospermaceae, Peganaceae, Tetradiclidaceae, Nyssaceae, Ternstroemiaceae, Pellicieraceae, Aucubaceae, Donatiaceae, Lobeliaceae, Desfontainiaceae, Diervillaceae, Dipsacaceae, Linnaeaceae, Morinaceae, and Valerianaceae. The other discontinued families were: Limnocharitaceae, Luzuriagaceae, Sparganiaceae, Ledocarpaceae, Heteropyxidaceae, Psiloxylaceae, Oliniaceae, Rhynchocalycaceae, Parnassiaceae, Maesaceae, Myrsinaceae, Theophrastaceae, Eremosynaceae, Polyosmaceae, Tribelaceae, Aralidiaceae, Mackinlayaceae, and Melanophyllaceae APG III CLASSIFICATION  20 families were accepted in the APG III system which had not been in the previous system, and a few families were moved to a different position. The newly recognized families are: Petermanniaceae, Schoepfiaceae, Limeaceae, Lophiocarpaceae, Montiaceae, Talinaceae, Anacampserotaceae, Centroplacaceae, Calophyllaceae, Guamatelaceae, Gerrardinaceae, Dipentodontaceae, Capparidaceae, Cleomaceae, Cytinaceae, Mitrastemonaceae, Metteniusaceae, Linderniaceae, Thomandersiaceae, and Quintiniaceae. The number of families not placed in any order was reduced from 39 to 10. Apodanthaceae and Cynomoriaceae were placed among the angiosperms, incertae sedis, that is, not in any group within the angiosperms. Eight other families were placed incertae sedis in various supra-ordinal groups within the angiosperms. The unplaced families were: Apodanthaceae, Cynomoriaceae, Dasypogonaceae, Sabiaceae, Dilleniaceae, Icacinaceae, Metteniusaceae, Oncothecaceae, Vahliaceae, and Boraginaceae. The circumscription of the family Icacinaceae remains especially doubtful. Apodytes, Emmotum, Cassinopsis, and a few other genera were provisionally retained within it until further studies can determine whether they properly belong there. APG III CLASSIFICATION  Three genera (Gumillea, Nicobariodendron, and Petenaea) were placed within the angiosperms incertae sedis. Gumillea had been unplaced in APG II. Nicobariodendron and Petenaea were newly added to the list. The classification is shown below in two versions. The short version goes to the level of orders and of families unplaced in an order. The detailed version shows all the families. Orders at the same level in the classification are arranged alphabetically. Note that orders may not contain the same families as in earlier versions of the APG system (APG system, APG II system).  Chase & Reveal ( 2009) gave a formal classification of land plants mainly considering the algae in APG III. To keep harmony between hierarchical classification and APG system, all land plants were included under Equisetopsida. Angiosperm are divided into 15 super orders. All total 56 orders are listed of which, two Chloranthales are unplaced . Further seven families could not be accommodated. APG III CLASSIFICATION MERITS OF THE CLASSIFICATION i. ii. iii. iv. v. vi. vii. viii. The system shows monophyly origin in groups, The system covers the multiple data from morphology, anatomy, embryology, phytochemistry & molecular data. Groups names up to orders have been assigned, Traditional divisions of the angiosperms into monocotyledons and dicotyledons has not been taken into account. Many monocots are put in between primitive angiosperms and eudicots. It can solve the problem of paraphyly among monocots and dicots in the early stages. A number of cladograms in the classification shows general affinities between the various groups of organisms. Primitive families are placed at the beginning of the angiosperms. The merger of Budlejaceae and Myotoraceae with Scrophulariaceae have been supported from morphological and molecular evidences given by Bremer et.al (2001) and Olmstead et.al (2001). Multigene analysis and morphological data are the basis on which Winteraceae and Cancellaceae are kept under the same order. MERITS & DEMERITS OF THE CLASSIFICATION         Family Agavaceae includes genera like Hosta, Camassina and Chlorogalum and it becomes more wide. This justification has been supported by Judd et.al (2002) and Thorne. Monophyletic concept is reflected in Malvaceae where families like Tiliaceae, Sterculariaceae and Bombaceae are included in the former. This inclusion is supported by molecular as well as morphological data. Asclepidaceae has been merged with Apocynaceae. This view is supported and strengthened by Judd et.al (1994) from molecular evidence. The concept of bracketed families in earlier APG has been removed in APG III. DEMERITS This classification is only applicable up to families. This system is not suitable for identification of flora in the true sense. The fate of some unplaced families and few replaced genera is still uncertain. Botanical nomenclature Code has not been assigned to new group. ACKNOWLEDGMENT  Google for images,  Different websites for content and enrichment,  Text Book of Plant Systematics- Chittaranjan Mohanty  Plant Taxonomy by O.P. Sharma,  Taxonomy of angiosperms- Nayek.  Plant Taxonomy- Gurucharan Singh  A text Book of Botany- Hait, Bhattacharyya & Ghosh  Advanced Plant Taxonomy- A.K. Mondal.  Disclaimer: This presentation has been developed to enrich free open source of the study materials for Biology students without any financial issues. THANK YOU FOR YOUR JOURNEY