ANGIOSPERMS PHYLOGENY GROUP IV SYSTEM OF CLASSIFICATION.pdf

Angiosperm plant classification is one of the important domains in plant taxonomy. The different taxonomists have given several systems from time to time since Aristotle. But the most modern approach in this regard is APG system and its latest version is APG IV has been given based on molecular data. This presentation offers a bird's eye view of plant classification in general and APG IV in particular along with merits and demerits.

1. A Presentation by:
Dr. N. Sannigrahi,
Associate Professor,
Department of Botany,
Nistarini College, Purulia (W.B)
723101, INDIA

2. Untildetailedgeneticevidencebecameavailable,theclassificationof
floweringplantswasbasedontheirmorphology(particularlythatofthe
flower)andtheirbiochemistry(whatkindsofchemicalcompoundthey
containedorproduced).
Classificationsystemsweretypicallyproducedbyanindividualbotanist
orbyasmallgroup.Theresultwasalargenumberofsuchsystems.
Differentsystemsandtheirupdatestendedtobefavoredindifferent
countries;e.g.theEnglersystemincontinentalEurope;theBentham&
HookersysteminBritain(particularlyinfluentialbecauseitwasusedby
Kew);theTakhtajansystemintheformerSovietUnionandcountries
withinitssphereofinfluence;andtheCronquistsystemintheUnited
States.
TheAngiospermPhylogenyGroup,orAPG,referstoaninformal
internationalgroupofsystematicbotanistswhocametogethertotryto
establishaconsensusviewofthetaxonomyoffloweringplants
(angiosperms)thatwouldreflectnewknowledgeabouttheirrelationships
baseduponphylogeneticstudies.

3. BenthamandHooker(1883)-202
EnglarandPrantle(1915)-303
ArthurCronquist(1981)-386
APGI(1998)-462
APGII(2003)-457
APGIII(2009)-415
APGIV(2016)-416.
TheClassificationofthefloweringplantseitherinthelineofphylogenyor
nothasexperiencedanumberofchanges,
TheAPGI,II,III,andIVhaveexperiencedanumberofnegativechanges
uptotheAPGIIIbutintheAPGIV,thereisalittlebitincreasesbyonlya
number1,
Thus,thesmallerfamilieshavebeengroupedintolargeroneforthesame
outcomes.
TotalAngiosperms=2,95.383speciesbelongsto13164generaoutof415
families(Monocots-74273;Eudicots-2,10,008)

4. TherearealtogetherfourversionsofAPGSystemofclassification-
APGI-1998
APGII-2003
APGIII-2009
APGIV-2016
Theallfourversionshavecometothedomainofplantclassificationto
exploretherecenttrendsofresearchinthecontextofplantphylogenywith
datainputs.
UnderstandingofAPGsystemneedstheconceptofthephylogenylines-
Monophyletic,PolyphyleticandParaphyletic
MONOPHYLETIC :Agrouporiginatedfromasingleancestoratasingle
timeinthepastbecausethepresentdayangiospermsshowremarkable
consistencyintheircharacterslikeuniformstaminalstructure,endothecial
layerintheantherwall,doublefertilization,formationoftriploid
endospermandpresenceofsievetubesinall.

5. POLYPHYLETIC:Whendicotsandmonocotsthoughttobeoriginatedat
differenttimesfromdifferentprimitivestocksandattainedtheirpresent
statusthroughparallelorconvergentevolution.Fossilrecordsvarietyin
perianthandthenatureofcarpelinbothdicotandmonocotsupportthe
theoryofpolyphylesis.
PARAPHYLETIC
Aparaphyleticgroupisagroupofanysizeandsystematicrankthat
originatedfromasinglecommonancestor,butdoesnot–asopposedtoa
monophyleticgroup–containalldescendantsfromthisancestor.The
ancestralspeciesofthisgroupisthusalsotheancestorofoneormoreother
groups.
Group should be Monophyletic.
A broad approach is taken to define the limits of groups such as families
and orders,

7. Aboveorparalleltoorderandfamilies,anothertermiscoinedknownas
“Clade”.
Theterm“Clade”wasfirstcoinedbyJulianHuxleyintheyear1957to
refertotheresultofCladogenesis.
Acladeisasinglebranch“ormonophyllumonthetreeoflife”i.e.
Cladograms(familytree)isofabiologicalgroup.
ThissystembasedonCladisticandPhylogeneticstudies,
Angiospermsarenotclassifiedintomonocotsanddicots,
Angiospermsaredirectlydividedintosuperorders,
Angiospermsaremonophyleticinorigin,
Themonophyleticoriginhasbeenstrengthenedonthebasisofthe
informationreceivedfromthedifferentbranchesofknowledgelike
morphology,anatomy,embryology,phytochemistry,palynology,
karyology,moleculardataandothers,

8. ThemoleculardatabasedonthechloroplastDNAusingRFLPtechnique,
ThemolecularstudieswerecarriedoutwithrespecttotheDNAsequences
oftwochloroplastgenes-atpBandrbcLalongwithonenucleargene,
nuclearribosome18SrDNA.
ThegenesatpBgenei.e.ATPasebetasub-unitgenehaving1540bp,rbcL
genei.e.Ribulose–biphosphatecarboxylaseFormLgenehaving1428bp
and18SrDNAi.e.18SRibosomalDNAhaving1855bp.
Totalbp=(1540+1428+18550bp)=4734bp.
Thus,theAPGsystemofclassificationconsistsofnumberofdiverse
charactersthathasmadeitmoreholisticincharacterstakingthefeaturesof
thedifferentsistersdomainofbiologicalsciences.

9. Itisconsideredas“referencetoolofbroadutility”.
Itconsiders40monophyleticordersand462families,
Uncertainpositionof25families,
Scientificnamesarenotusedabovetherankoforder;cladeisbeingused,
Alternateclassificationofthesamegroupisused;smallerfamiliestobe
includedintolargerfamilies.e.g.Fumariaceaecanbetreatedasseparate
familyortobeincludedunderthefamilyPapaveraceae,
Traditional;divisionofangiospermsintomonocotsanddicotswere
abolished;monocotswastreatedasseparateclade,
Dicotsarenottreatedasseparateclade;insteadofthat,itisEudicotsor
truedicots.

10. PeterStevensquestionedthevalidityofdiscussionregardingfamily
delimitationintheabsenceofchangersofPhylogeneticrelationship.
Thelargegenebanksofplastid,mitochondriaandnuclearribosomewere
considered.
Usesofalternative“Bracketed”taxaallowingthechoiceofeitheralarge
familyoranumberofsmallerones.Forexample,thelarge‘Asperagaceae
‘familyincludes7‘Bracketed’familieswhicheithercanbeconsideredas
Asperagaceaefamilyorasseparatefamilies.
Newordersareproposedandpreviouslyunplacedfamiliesplacedinthe
systemofAPGII,
Severalmajorfamilieswererestructured,
APGIIrecognized45orders;5morethanthatoftheAPGIsystemof
classification,
5neworderswereintroduced.Allofwhichfamilieswereunplacedasto
orders,
APGIIrecognized457familiesandthenumberofthefamiliesreducedby5as
theordershaveincreased,
55Familieswereincludedunder“Bracketed”families

11. Thenumberofordergoesupto59whichwas10morethantheprevious
one.
10familiesarenotplacedinanorderandonlytwoofthese-
ApodanthaceaeandCynomoriaceaeareleftentirelyoutsidethe
classification.
14neworderswereaccepted,
Thedesignationof“AlternativeBracketed”familieswasnotusedinAPG
III.
Reducednumberfamiliesreachedto415,ratherthan457ofAPGIIas
statedbefore,
10familiesunplacedinanorder,
21newfamiliesaccepted,
ThreegeneralikeGumillea,NicobariodendronandPetenaeawereplaced
withinangiospermsincertaesedis(ofuncertainplacemen).

12. TheAngiospermPhylogenyGroupIVsystemoffloweringplant
classificationisthefourthversionofamodern,mostlymolecular-based,
systemofplanttaxonomyforfloweringplants(angiosperms)being
developedbytheAngiospermPhylogenyGroup(APG).
TheAngiospermPhylogenyGroupIVsystemoffloweringplant
classificationisthefourthversionofamodern,mostlymolecular-based,
systemofplanttaxonomyforfloweringplants(angiosperms)being
developedbytheAngiospermPhylogenyGroup(APG).
Thegeneralschemeofthearrangementofmajorgroupswasalsoclear:a
gradeofisolatedtaxa(theANAgrade,orANITAgradeasitwasthen
called)leadingtothemajorradiationofangiosperms,acladeofall
monocots,acladeofMagnoliidfamiliesandalargeEudicots(tricolpate)
cladecomposedofseveralsmallcladesandtwomajorgroups,rosidsand
asterids,eachcomposedoftwomajorsub-clades.

14. TwoadditionalinformalmajorClades-SuperrosidesandSuperasteriods
hasbeenrecognized,
5newordershasbeenaccepted,
Nowthenumberofordersgoesupto64andfamiliesto416,
Potentiallymonofamilialorders-DasypogonaceaeandSabiaceae,are
insteadreferstoArecalesandProtealesrespectively,
Twoparasiticfamiliesplaced:CynomoriaceaeinSaxifragalesand
ApodanthaceaeinCucurbitales,
NochangesisrecognizedinDiosorealesandSantalales,
SubstitutingAsphodelaceaeforXanthorrhoeaceae(Asparagales)and
FrancoaceaeforMelianthaceae(Geraniales),
SeveralgeneraoffamilyIcacinaceaeweremovedtoMetteniusaceae,
SomegenerastillremainsunplacedlikePeltanthera,Lamiales.
Thediversityoffloweringplantsisnotevenlydistributed,
NearlyallspeciesbelongstoEudicots(75%),monocot(23%)and
Magnoliid(2%)

15. Theremaining5Cladescontainalittleover250speciesamong9families
whichislessthan0.1%ofthefloweringdiversity.
GENERALOUTLINEOFTHEAPGIVCLASSIFICATION
AngiospermsdividedintoEarlyangiosperms,MonocotsandEudicots,
EARLYANGIOSPERMS-8orders&26familiesconsistsofANAGrade+
Magnoliids+Choranthales,
MONOCOTS-11Ordersand77FamiliesconsistsofBasalMonocots,
LilioidsandCommelinids,
EUDICOTS-Consistsof45Ordersand313Families,
ItisfurtherdividedintoEarlyDivergingEudicots,SuperRosidsandsuper
Asterids,
EarlydivergingEudicots–7Orders&17FamiliesincludingEED+
Ceratophyllales+Dilleniales,
SuperRosids-18ordersand150familiesconsistsofSaxifragales+Rosidas
(17Orders&135FamiliesincludesVitales+Fabids+Malvids)

16. SERIALNO 0rders No 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

17. Name of the family Genera Species
Orchidaceae 736 28000
Asteraceae 1623 24700
Fabaceae 751 19500
Rubiaceae 590 13620
Poaceae 780 12000

18. Theunderstandingoftheconceptofphylogenyingeneraland
primitivenessinparticularwasaseriousconcernandnumberoftheories
havebeenputforwardinordertoextinguishtheproblemsbythedifferent
phylogenistsfromtimetotime.
TheAPGsystemhasbroughtmanychangesinthisaspectasstatedbelow.
Monocotsaretreatedasmonophyleticinoriginandhencetheterminology
wasretained,
TherealRanaleanfamiliesespeciallythearborescentonearenomorethe
primitivefamiliesasperAPGsystem.Accordingtothissystemof
classification,Arborellaceae,Nymphaceae,Magnoliaceae,Chloranthaceae
formtheearlyangiosperms,
Dicotsarepolyphyleticgroup.Asaconsequence,theuseofterm
Dicotyledonsneednolongerinuse,insteadofEudicots,
Liliaceousissplitinto14families,
MolluginaceaeandGisekiaceaearerecognizedseparatelyfromAizoaceae,

19. EuphorbiaceaeissplitintoPhyllanthaceae,Picrodendraceaeand
Putranjivaceae,
BrassicaceaeissplitintothreefamilieslikeBrasicaceae,Cappraceaeand
Cleoamaceae,
AsclepiadaceismergedintoApocynaceae,
ChenopodiaceaeismergedwithAmaranthaceae,
Bombacaceae,SterculiaceaeandTiliaceaearemergedintoMalvaceae,
ManygenerathatareconventionallytreatedintoVerbenaceaesuchas
Clerodendron,VitexandTectonaaretransferredintoLamiaceaebasedon
themodificationofthecircumscriptionofthesefamilies.
Thus,agrosschangesarenoticedintheAPGsystemofclassificationand
thestatusofanumberofgenerahavebeenchangesaccordingly.

20. Thesystemshowsmonophylyoriginingroups,
Thissystemisbasedonmmoleculardata.
Familieswithprimitivecharacterswereplacedinthebeginning,
APG IV adopts phylogenetic principles of monophyly.
DEMERITS
Thisclassificationisonlyapplicableuptofamilies.Thissystemisnot
suitableforidentificationofflorainthetruesense.
Thefateofsomeunplacedfamiliesandfewreplacedgeneraisstill
uncertain.
BotanicalnomenclatureCodehasnotbeenassignedtonewgroup,
Notverypopular,difficultintheuseinHerbaria

22. Googleforimages,
Differentwebsitesforcontentandenrichment,
TextBookofPlantSystematics-ChittaranjanMohanty
PlantTaxonomybyO.P.Sharma,
Taxonomyofangiosperms-Nayek.
PlantTaxonomy-GurucharanSingh
AtextBookofBotany-Hait,Bhattacharyya&Ghosh
AdvancedPlantTaxonomy-A.K.Mondal.
Disclaimer:Thispresentationhasbeendevelopedtoenrichfreeopen
sourceofthestudymaterialsforBiologystudentswithoutanyfinancial
issues.