ANGIOSPERMS PHYLOGENY GROUP IV SYSTEM OF CLASSIFICATION.pdf

ANGIOSPERMS PHYLOGENY GROUP IV SYSTEM OF CLASSIFICATION.pdf

• 1.
  A Presentation by: Dr.N. Sannigrahi, Associate Professor, Department of Botany, Nistarini College, Purulia (W.B) 723101, INDIA
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   Until detailedgenetic 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.
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   Bentham andHooker (1883)- 202  Englar and Prantle (1915)- 303  Arthur Cronquist(1981)-386  APG I (1998)-462  APG II (2003)-457  APG III (2009)-415  APG IV( 2016)-416.  The Classification of the flowering plants either in the line of phylogeny or not has experienced a number of changes,  The APG I, II, III, and IV have experienced a number of negative changes up to the APG III but in the APG IV, there is a little bit increases by only a number 1,  Thus, the smaller families have been grouped into larger one for the same outcomes.  Total Angiosperms= 2,95. 383 species belongs to 13164 genera out of 415 families (Monocots-74273; Eudicots-2,10,008)
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   There arealtogether four versions of APG System of classification-  APG I-1998  APG II- 2003  APG III-2009  APG IV-2016  The all four versions have come to the domain of plant classification to explore the recent trends of research in the context of plant phylogeny with data inputs.  Understanding of APG system needs the concept of the phylogeny lines- Monophyletic, Polyphyletic and Paraphyletic  MONOPHYLETIC: A group originated from a single ancestor at a single time in the past because the present day angiosperms show remarkable consistency in their characters like uniform staminal structure, endothecial layer in the anther wall, double fertilization, formation of triploid endosperm and presence of sieve tubes in all.
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   POLYPHYLETIC: Whendicots and monocots thought to be originated at different times from different primitive stocks and attained their present status through parallel or convergent evolution .Fossil records variety in perianth and the nature of carpel in both dicot and monocot support the theory of polyphylesis.  PARAPHYLETIC  A paraphyletic group is a group of any size and systematic rank that originated from a single common ancestor, but does not – as opposed to a monophyletic group – contain all descendants from this ancestor. The ancestral species of this group is thus also the ancestor of one or more other groups.  Group should be Monophyletic.  A broad approach is taken to define the limits of groups such as families and orders,
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   Above orparallel to order and families, another term is coined known as “Clade”.  The term “Clade” was first coined by Julian Huxley in the year 1957 to refer to the result of Cladogenesis.  A clade is a single branch “ or monophyllum on the tree of life” i.e. Cladograms (family tree) is of a biological group.  This system based on Cladistic and Phylogenetic studies,  Angiosperms are not classified into monocots and dicots,  Angiosperms are directly divided into super orders,  Angiosperms are monophyletic in origin,  The monophyletic origin has been strengthened on the basis of the information received from the different branches of knowledge like morphology, anatomy, embryology, phytochemistry, palynology, karyology, molecular data and others ,
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   The moleculardata based on the chloroplast DNA using RFLP technique,  The molecular studies were carried out with respect to the DNA sequences of two chloroplast genes- atpB and rbcL along with one nuclear gene, nuclear ribosome 18S rDNA.  The genes atpB gene i.e. ATPase beta sub-unit gene having 1540 bp, rbcL gene i.e. Ribulose –biphosphate carboxylase Form L gene having 1428 bp and 18S rDNA i.e. 18S Ribosomal DNA having 1855 bp.  Total bp= (1540+1428+18550bp)=4734 bp.  Thus, the APG system of classification consists of number of diverse characters that has made it more holistic in characters taking the features of the different sisters domain of biological sciences.
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   It isconsidered as “reference tool of broad utility”.  It considers 40 monophyletic orders and 462 families,  Uncertain position of 25 families,  Scientific names are not used above the rank of order; clade is being used,  Alternate classification of the same group is used; smaller families to be included into larger families.e.g. Fumariaceae can be treated as separate family or to be included under the family Papaveraceae,  Traditional; division of angiosperms into monocots and dicots were abolished; monocots was treated as separate clade,  Dicots are not treated as separate clade; instead of that, it is Eudicots or true dicots.
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   Peter Stevensquestioned the validity of discussion regarding family delimitation in the absence of changers of Phylogenetic relationship.  The large gene banks of plastid, mitochondria and nuclear ribosome were considered.  Uses of alternative “Bracketed” taxa allowing the choice of either a large family or a number of smaller ones. For example, the large ‘Asperagaceae ‘family includes 7 ‘Bracketed’ families which either can be considered as Asperagaceae family or as separate families.  New orders are proposed and previously unplaced families placed in the system of APG II,  Several major families were restructured,  APG II recognized 45 orders; 5 more than that of the APG I system of classification,  5 new orders were introduced . All of which families were unplaced as to orders,  APG II recognized 457 families and the number of the families reduced by 5 as the orders have increased,  55 Families were included under “Bracketed” families
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   The numberof order goes up to 59 which was 10 more than the previous one.  10 families are not placed in an order and only two of these- Apodanthaceae and Cynomoriaceae are left entirely outside the classification.  14 new orders were accepted,  The designation of “Alternative Bracketed” families was not used in APG III.  Reduced number families reached to 415, rather than 457 of APG II as stated before,  10 families unplaced in an order,  21 new families accepted,  Three genera like Gumillea, Nicobariodendron and Petenaea were placed within angiosperms incertae sedis ( of uncertain placemen).
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   The AngiospermPhylogeny Group IV system of flowering plant classification is the fourth version of a modern, mostly molecular-based, system of plant taxonomy for flowering plants (angiosperms) being developed by the Angiosperm Phylogeny Group (APG).  The Angiosperm Phylogeny Group IV system of flowering plant classification is the fourth version of a modern, mostly molecular-based, system of plant taxonomy for flowering plants (angiosperms) being developed by the Angiosperm Phylogeny Group (APG).  The general scheme of the arrangement of major groups was also clear: a grade of isolated taxa (the ANA grade, or ANITA grade as it was then called) leading to the major radiation of angiosperms, a clade of all monocots, a clade of Magnoliid families and a large Eudicots (tricolpate) clade composed of several small clades and two major groups, rosids and asterids, each composed of two major sub-clades.
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   Two additionalinformal major Clades - Superrosides and Superasteriods has been recognized,  5 new orders has been accepted,  Now the number of orders goes up to 64 and families to 416,  Potentially monofamilial orders- Dasypogonaceae and Sabiaceae , are instead refers to Arecales and Proteales respectively,  Two parasitic families placed: Cynomoriaceae in Saxifragales and Apodanthaceae in Cucurbitales,  No changes is recognized in Diosoreales and Santalales,  Substituting Asphodelaceaefor Xanthorrhoeaceae (Asparagales) and Francoaceae for Melianthaceae (Geraniales),  Several genera of family Icacinaceae were moved to Metteniusaceae,  Some genera still remains unplaced like Peltanthera , Lamiales.  The diversity of flowering plants is not evenly distributed,  Nearly all species belongs to Eudicots (75%), monocot (23%) and Magnoliid (2%)
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   The remaining5 Clades contain a little over 250 species among 9 families which is less than 0.1% of the flowering diversity.  GENERAL OUTLINE OF THE APG IV CLASSIFICATION  Angiosperms divided into Early angiosperms, Monocots and Eudicots,  EARLY ANGIOSPERMS- 8 orders & 26 families consists of ANA Grade+ Magnoliids +Choranthales,  MONOCOTS- 11 Orders and 77 Families consists of Basal Monocots, Lilioids and Commelinids,  EUDICOTS- Consists of 45 Orders and 313 Families,  It is further divided into Early Diverging Eudicots, Super Rosids and super Asterids,  Early diverging Eudicots – 7 Orders & 17 Families including EED+ Ceratophyllales +Dilleniales,  Super Rosids- 18 orders and 150 families consists of Saxifragales +Rosidas (17 Orders & 135 Families includes Vitales + Fabids +Malvids)
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  SERIAL NO 0rdersNo of Families No of Genera No of Species 1. Asparagales 14 1122 36205 2. Asterales 11 1743 26870 3. Lamiales 24 1059 23810 4. Fabales 04 754 20140 5. Gentianales 05 1121 19915 6. Poales 15 997 18875 7. Malpighiales 36 716 16065 8. Myrtales 09 380 13005 9. Caryophyllales 37 749 11620 10 Ericales 22 346 11545
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  Name of thefamily Genera Species Orchidaceae 736 28000 Asteraceae 1623 24700 Fabaceae 751 19500 Rubiaceae 590 13620 Poaceae 780 12000
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   The understandingof the concept of phylogeny in general and primitiveness in particular was a serious concern and number of theories have been put forward in order to extinguish the problems by the different phylogenists from time to time.  The APG system has brought many changes in this aspect as stated below.  Monocots are treated as monophyletic in origin and hence the terminology was retained,  The real Ranalean families especially the arborescent one are no more the primitive families as per APG system. According to this system of classification, Arborellaceae, Nymphaceae, Magnoliaceae, Chloranthaceae form the early angiosperms,  Dicots are polyphyletic group . As a consequence, the use of term Dicotyledons need no longer in use , instead of Eudicots,  Liliaceous is split into 14 families,  Molluginaceae and Gisekiaceae are recognized separately from Aizoaceae,
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   Euphorbiaceae issplit into Phyllanthaceae, Picrodendraceae and Putranjivaceae,  Brassicaceae is split into three families like Brasicaceae, Cappraceae and Cleoamaceae,  Asclepiadace is merged into Apocynaceae,  Chenopodiaceae is merged with Amaranthaceae,  Bombacaceae, Sterculiaceae and Tiliaceae are merged into Malvaceae,  Many genera that are conventionally treated into Verbenaceae such as Clerodendron, Vitex and Tectona are transferred into Lamiaceae based on the modification of the circumscription of these families.  Thus, a gross changes are noticed in the APG system of classification and the status of a number of genera have been changes accordingly.
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   The systemshows monophyly origin in groups,  This system is based on m molecular data.  Families with primitive characters were placed in the beginning, APG IV adopts phylogenetic principles of monophyly.  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,  Not very popular , difficult in the use in Herbaria
• 22.
   Google forimages,  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.