ORIGIN& EVOLUTION OF ANGIOSPERMS.pdf

This PPT offers a magical journey of the magic of the reality of the origin & evolution of Angiosperms.

1. A BIRD’S EYE VIEW
ORIGIN & EVOLUTION OF ANGIOSPERMS

4. Angiospermsorfloweringplantsformthelargestgroupofplantkingdom,
includingabout300families(411families,Hutchinson),8,000generaand
300,000species.Theyareconsideredtobehighestevolvedplantsonthe
surfaceoftheearth.FromCretaceousage,theangiospermseclipsedallother
vegetationandnowtheyaredominant.Theyarefoundalmosteverywherein
eachpossibletypeofhabitatandclimate.Theyoccurindeeplakes,deserts,in
bedsofseasandevenonhighpeaksofmountains.ThespeciesofOpuntia
(Cactaceae)cansurvivewithoutwaterinacutedesertconditions,whereason
theotherhandthespeciesofHydrilla(aquaticplant)areextremelysensitiveto
droughtconditions.Somespeciesarefoundonrocks,someinwaterfallsand
alsosomearemarine.ThespeciesofRhizophora,popularlyknownas
‘mangrovevegetation’arefoundnearthewaterofthesea.Theepiphytes,
parasites,saprophytes,symbiontsandeveninsectivorousplantsarealsonot
uncommon.Theymaybeannual,biennialorperennialherbs,shrubs,trees,
climbers,twinersandlianas.Ononehandtheangiospermsmaybeasminute
insizeasapinhead,e.g.,Wolffiamicroscopica,ontheotherextremitylike
EucleptilesofAustraliamayreachupto300feetinheight.

5. i.Thesporophytewhichisthedominantplantinthelife-cycleis
differentiatedintoroots,stemandleaves.
ii.Thehighestdegreeofperfectionofthevascularsystemwithtruevessels
inthexylemandcompanioncellsinthephloem.
iii.Theorganizationofthemicrosporophyll’s(stamens)and
megasporophylls(carpel)intoastructurecalledtheflower,whichis
typicalonlyoftheangiosperms.
iv.Thepresenceoffourmicrosporangia(pollensacs)permicrosporophyll
Theovulesarealwaysenclosedinanovarywhichisthebasalregionof
themegasporophyll.
v.Productionoftwokindsofspores,microspores(pollengrains)and
megaspores.Angiospermsthusareheterosporous.
vi.Presenceofsinglefunctionalmegasporewhichispermanentlyretained
withinthenucellusormega-sporangium.
vii.Adaptationofflowertoinsectpollination.
viii.Pollinationconsistsinthetransferenceofpollengrainsfromantherto
stigma.

6. X.Extremereductioninsize,durationofexistenceandcomplexityofthe
structureofthegametophyteswhichareentirelyparasitic.
XI.Themalegametophytehasreachedthelimitsofreduction.Itconsistsonly
ofthepollengrainandthepollentubecontainsthetubenucleusandtwo
malegametesornuclei.Themalecells(gametes)arenon-ciliated.
XII.Thefemalegametophytelacksanyextensivedevelopmentofvegetative
tissue.Itconsistsofthreeeggapparatuscells,threeantipodalcellsand
twopolarnucleiinthecentreoftheembryosac.
XII.Thenon-motilemalecellsornucleiarecarriedbodilytotheneighborhood
ofeggapparatusbythepollentube.
XIV.Theseedorseedsremainenclosedintheripenedovarycalledthefruit.
XV.Thephenomenonofdoublefertilizationortriplefusionisthe
characteristicoftheangiosperms.
XVI.Theendospermdevelopsafterfertilization.Itistriploid.
XVII.Theangiospermsarecompletelyadaptedtolifeonland.
XVIII.Sporedimorphisimhavingresultedintheproductionofgametophytes,
maleandfemale

7. TheangiospermsappearedsuddenlyinCretaceousageabout65million
yearsback.CharlesDarwindescribedthissuddenappearanceof
angiospermsinlowerorupperCretaceousasan‘abominablemystery.
Whenangiospermsappearedforthefirsttimeinlowerorupper
Cretaceous,theywerefullfledgedlikethetreesandtheherbsoftoday.In
supportofthisviewProf.Knowltonadvocatesinhis‘Plantofthepast’,
“fromthetimeoftheirappearancetheydidnotprogressatalldueto
theirfull-fledgedappearanceintheCretaceous”.
Thefossilrecordsoftheangiospermsalsosupporttheirappearancefull-
fledgedinlowerorupperCretaceous.Thefossilsofthatageareso
characteristicandmodeminappearancethatmostofthemcanbereferred
unmistakablytolivingfamilies,generalandeventosomespecies.
Theformsofcycadsandconifers,whichlongdominatedtheuniversewere
alreadypushedbackgroundandtheearthhadbecomeinfacttheearthof
floweringplants.CharlesDarwinhascalledthissuddenappearanceof
angiospermsasan“abominablemystery”.

8. However,someworkersdonotagreewiththedoctrineof‘abominable
mystery’.AccordingtoH.H.Thomas(1936),theangiospermsofthepast
replacedmanyofoldergymnospermsinestuarineandmarshywaters.
GraudEury(1906)believesthattheangiospermscameintoexistence
throughmutation.Guppy(1919)however,supportedtheviewofmutation.
Prof.Bertrandisofopinionthatallthegreatgroupsofvascularplants
(Pteridophyta,GymnospermandAngiosperms)notonlyarosequite
independentlyofeachotherbutalsotheyoriginatedsimultaneouslyasfar
backintheArchianperiod(2000millionyearsold-oldest)
Thesepossibilitiesare:
1.Thattheangiospermsaremonophyleticintheiroriginbuthavehada
verymuchlongerhistorythanatpresentknown,perhapsstretchingback
intoPaleozoictimesandwithawholeseriesofmissinglinks;
2.Thattheangiospermsaremonophyleticbutthatthefirstandatpresent
unknowngroupdivergedquicklyintermsofgeologicaltime,intoa
considerablenumberofdifferentgroups;
3.Thattheangiospermsarepolyphyletic.

9. HOMOLOGY istheresemblancebetweentwoorganismsdueto
inheritancefromacommonancestry.•Characterswithsameorigin,but,
differentinappearanceorfunction•Theresemblancesduetohomologyare
real.•Homologybetweentwoorganismscanresultonlyfromtheirhaving
evolvedfromacommonancestor,andtheancestormustalsocontainthe
samefeatureorfeaturesforwhichthetwoorganismsarehomologous.
Throughdivergentevolution,organismsmaydevelophomologous
structures.
ANALOGY•Analogyistheresemblancebetweentwoorganismsdueto
functionalsimilarityandnotduetoinheritancefromacommonancestry.•
Characterswithdifferentorigin,but,similarinappearance.•The
resemblancesduetoanalogyaregenerallysuperficial.•Analogybetween
twoorganismscanbeduetosuperficialresemblance,i.e.,occurrenceofa
partoranorganinoneorganismwhichhasthesamefunctionasanother
partororganinadifferentorganisms.

10. Darwin(1959)definedhomologyasthatrelationshipbetween
whichresultsfromtheirdevelopmentfromthecorresponding
embryonicpartsbutSimpson(1961)statedthatthehomology
istheresemblanceduetoinheritancefromacommon
ancestryandanalogyistheresemblancefromfunctional
aspectbutnotduetoinheritancefromacommonancestry.
Wilen(1981)statedthatthehomologymayarisebetween
twocharacters,twocharactersstatesorbetweentwo
organismsforaparticularcharacterstate.Twocharactersare
homologousifoneisdirectlyderivedfromtheother.These
seriesofcharactersinquestionarecalledmorphoclinesor
phenoclines.Theoriginalpre-existingcharacteriscalledas
plesiomorphicandthederivedoneasapomorphic.Thetwo
termsapomorphicandplesiomorphicmayberelative.

11. In‘Parallelism’,theorganismshaveacommonancestorbutthe
character-statewasnotpresentintheircommonancestorwhilein
convergence,twodifferentcharactersindifferentancestorsevolving
identicalcharacter–states.AccordingtoSimpson(1961)parallelismis
definedastheindependentoccurrenceofsimilarchangesingroupswith
acommonancestry.InRananculustwospeciesR.tripartiusandR.
hedevaceahavesimilarcharactersofaquatichabitanddissectleaves
whichhappenduetoparallelevolution.IncaseofGentumand
Dicotyledonswithrelatedvessels,thereisparallelism.
Whileconvergence,similarityisobservedbetweenthetwodistinct
phyleticlineswithregardtoindividualorganortothewholeindividual.
Similarfeaturesariseseparatelyintwoormoregeneticallydiverseand
notrelatedtaxaorlineages,IncaseofOchidaceae&Asclepiadaceae,
polliniaisfoundanditshowsdivergence.

12. Ingeneral,monophylyreferstoderivationfromasingleancestor
whereaspolyphylyreferstoderivationfrommorethanoneancestor.In
paraphyly,alldescendentsofthemostrecentcommonancestorsare
keptinthegroup.
Simpson(1961)definedmonophylyasthedeviationofataxonthrough
oneormorelineagesordescendentsfromtheimmediatelyancestral
taxonofthesameorthelowerrank.Letoneexample-saygenusBhas
beenderivedfromthegenusAthroughasinglespecies.Thegenusis
monophyleticatthegenusaswellasspecieslevel.Itevolvedfromthe
twospeciesofAitshowsmonophyleticoriginatgenuslevelbut
polyphyleticatthelowerrankthatisatthespecieslevel.
Therearetwodifferentlevelsofmonophyly-aminimummonophyly
andstrictmonophyly.Incaseofformerone,onesupraspecifictaxonis
derivedfromanequalrankbutincaseoflatter,highertaxonisderived
fromasingleevolutionaryspecies.

13. Henningdefinedmonophyleticgroupasagroupofspeciesdescendedfrom
asinglespeciesandwhichincludedallthedescendentsfromthisspecies.
Inasimplerway,alldescendentsofaspeciesatatimeareplacedina
monophyleticgroupTwotypeofmonophyleticgroupshasbeen
demarcated-holophyletic&paraphyletic.Inholophyletic,allthe
descendentsofthemostcommonancestorremaininthegroup.In
paraphyletic,alldescendentsofthemostrecentcommonancestorarenot
includedinthegroup.Inotherwords,aparaphyletictaxonisonethat
includesthemostcommonancestor,butnotallthedescendents.A
paraphyleticisdefinedasonethatdoesnotincludethecommonancestor
ofthemembersofthetaxon.Now,theholophyleticandmonophyleticare
synonymous.

14. Withinacladograms,abranchthatincludesasinglecommonancestorand
allofitsdescendantsiscalledaclade.Acladogramsisanevolutionarytree
thatdiagramstheancestralrelationshipsamongorganisms.AGroupof
individualsproducingsuccessively,similarandgeneticallyrelated
individualsarecalledClades.Acladecanberepresentedbytheline
diagramiscalledcladogramswhichshowswoodyhabit,alternateleaves,
cymoseinflorescence,5redpetals,5stamens,2freecarpelsanddryfruit
withmanyseedsinsideit.Aphylogenetictreedepictsphylogenetictree.
Theverticalaxisshowsthegeologicperiod.Thebranchinthetree
representstheoriginofthegroupandtheterminalportionindicatestheend
ofthegroup.Thebranchingemergesfromthemainaxisarethefossil
groupswhichendinthegeologictimewhenthegroupbecomeextinct.

15. Livinggroupsaremarkedbytheirdistancefromthecentre.Primitive
groupsareclosetothecentreandtheadvancedgroupsremaintowardsthe
periphery.Thebranchingdiagramsarecalleddendrograms.
Wiley(1981)definesphylogenetictreeasabranchingdiagramportraying
hypothesizedeventslinkingindividualorganisms,populationor
taxa.Accodingtohim,itisbranchingdiagramofentitieswherethe
branchingisbasedoninferredhistoricalconnectionsbetweentheentities
asevidencedbythesynapmorphies.Itisthus,aphylogeneticorhistorical
dendrogram.Recentlyalltheevolutionarydiagramsaredrawnareknown
asevolutionarytreeorphyletictree.Thesearesynonymouswith
cladograms.

17. InBiology,evolutionisthechangeinheritablecharacteristicsofbiological
populationsoversuccessivegenerations.Thesecharacteristicsarethe
expressionsofgenes,whicharepassedonfromparenttooffspringduring
reproduction.Evolutionisthemostinterestingdomainofthebiologyasit
inducestoexplorethemagicoftherealityoflifesincethetimeimmemorial
alongwiththeirchangeswiththepassageoftimeduringthegeological
period.Themostdominantgroupoftheplantkingdomwithsomeunique
featuresinducesanumberofquestionsregardingitsoriginandevolutionas
thescantyfossilrecordsareenoughtocomeanyclearcutdistinct
conclusion.Aformgenus,ClavitopollenitesreportedbyCouper(1958)from
BerremianandAptianstratabelongingtotheearlyCretaceousofEngland
about132-112mYisthemostimportantexamplesinthisregard.Many
fossilsshowtheherbaceousnatureofangiospermssimilarwith
Magnoliidae,Magnoliales,Lauralesetcandthelatecretaceouseracontains
50%fossilsbeingangiosperminnature.Archaestrobiluscupulanthus,a
formgenushasresemblancewithWelwitschia,agymnospermoflate
TriassicofTexaswithspirallyarrangedmacrocupulesonconstructedmale
andfemalespikes.

18. Withthehelpofseveralfindings,itcanbeconcludedthatthereare
twoprobabledatesregardingtheoriginofangiosperms.-oneinthe
Triassic
whenstemangiospermsreportedbyDoyleandDonoghuein1993
as‘angiophytes’andthesecondonereferstocrowngroupof
angiospermsoflateJurassicperiodthatsplitsintoextantsubgroups.
1.Axelrod(1970)proposedtheoriginofangiosperminmilduplands
atlowlatitudes,
2.SoutheastAsianeartoMalaysiaasthesiteoftheoriginby
Smith,1970,
3.AccordingtoStebbins(1974),ithasbeenevolvedunder
environmentalstressanddrought,
4.Bailey&Takhtajan(1969)studiesthefloraofSouthernPacific
Islandsandsuppliedthemissinglinkasthepolyphyleticoriginof
angiosperms.

19. Althoughtheoriginofangiospermsisanabominablemystery,
thereartetwoschoolsofthoughts-Monophyletic&polyphyletic
origin.Hutchinson(1973),Thorne(1983-2007).Takhtajan(1997),
Bremeretal.APGII,2003andothersinfavoroftheMonophyletic
originofangiospermsandtheyproposedthatmonocotyledons
haveevolvedfromtheirprimitivedicotyledonsandthisisbased
onsievetubes,companioncells,closedcarpels,8nucleateembryo
sac,reducedgametophytes,triploidendosperm.Sporne(1974)
viewedthatgymnospermsaretheancestorsofangiospermsand
independentdevelopmentofcharacterstookplaceinthepassage
ofevolution.Melville(1983)arguesforthepolyphyleticoriginand
theGlosspteridaeistheancestorofmanyangiosperms.Campbell
(1930)believedthatangiospermmighthavebeenevolvedfrom
pteridophytesduetotheirsimilaritywitheusporangiatefernsand
monocotyledonshavebeenevolvedfromIsoetesasfarasthe
positionofembryosac,modeoflateralgrowthandformationof
stemapexasinAlisma&Isoetesalthoughitwasrejectedbythe
groupofphylogenists.

20. 1.Pteridospermtheory:Onthebasisofhistologyandstellar
structure(Andrew,1947;Arnold,1949;Cronquest,1968)),seed
fernsarethoughttobeancestorofangiosperms.Inboththecases,
eusporangiatetypedevelopment,twotracestoonegapand
amphiphloicstele,theysharesomecommoncharactersandthe
laminartypeofplacentationissomehowrelatedtothesoral
distributionoftheferns.Butthesimplestructureofangiosperm
ovuleandcomplexseedofpteridophytesarepointsof
disagreement.
2.Anthrostrobilustheory:Angiospermflowerevolvedfroman
unbranchedbisexualstrobilusbearingspirallyarrangedpollen
andovulateorgans.Itgotsimilaritywiththereproductive
structureofancientBennettitaleangymnosperms.Bisexual;
flowersofMagnolialesseemstohaveevolvedfromsuchstock.
Bennettialeanoriginalongwithseedbearingorgans,Caytonia
andleafstructureofcycasshowadegreeofsimilarityinthis
regard.

21. 3.PseudanthialTheory:AngiospermstookoriginfromGnetopsidaas
proposedbyWettstein(1907)fromthestockslikeEphedra,Gnetumand
Welwitschiaduetothefollowingresemblances-
Reticulatedicot-likeleavesinGnetum,
Presenceofvessels,
Maleflowerwithperianthandbract,
Reductioninmalegametophytewithventralcanalnucleus,
EphedrashowsCasuarinaslikehabit
HomologybetweencompoundstrobilusofGentaleswiththeinflorescence
ofwindpollinatedAmentiferaealongwithinsectpollinatedbisexualflowers
ofMagnolia.ThistheorywasnotsupportedbyCarlquist(1996),Young
(1981)andothers.ButCornet(1996)discoveredWelwitschialikefossils
ArchaestrobiluscupularanthusandthisstrengthentheGnetopsidaoriginof
angiosperms.Themaleandfemalespikesoffossilplantpossessmany
spirallyarrangedmicrocupules.Eachmacrocupulecarriedanovule
surroundedbysterilescales.Withthesefeatures,Gentospdaconsideredtobe
closememberofangiosperms.

22. 4.AnthocormTheory:Itisbasedonpolyphyleticoriginofangiosperms
proposedbyNiemeyer(1924).Asfarasthistheory,theangiospermflowerhas
severalseparateorigin.InMagnoliidaeandtheirderivatives,theyaremodified
pluriaxialsystemi.e.holoanthocormswhicharethoughttobederivedfrom
gnetopsidaviathepiperales.Buttheoriginalmodifieduniaxialsystemi.e.
gonocladsoranthroidgaverisetotheflowerofChloranthaceae.Meeuse
(1963)advocatedfortheoriginofmonocotyledonsfromthefossilorder
PentoxyalesthroughmonocotorderofPandanales.ThePentoxylaleswere
woodyplantsandtheirstemhadmanyconductingstrandseachwithits
cambium.Thefeaturegivesaclueforthelinkwiththemanymonocotyledons
duetotheirmanyvascularbundlesinthestem.TheleafgenusOfPentoxylon
knownasPentophyllumthatarestarshapedandhadadominantmidribwith
parallelvenation.Thepollenbearingorgans.Sahaniaweresimilartothe
Bennettiales.TheseedbearingstructurewassimilartoMulberryandtheouter
fleshysarcastawasconsideredhomologoustothecupuleoftheseedferns.
TaylorandHickey(1996)excludedPentoxylonfromAnthophytesthroughthe
lattercontainsangiospermlineageanditssistergroupsBenenettialesand
Genetopsida.

23. 5.GonophyllTheory:thistheorywasputforwardedbyMelville(1962,
63,83)onthebasisoftheangiospermwasaleafwithanepiphyllous
fertilebranchknownasgonophyll.Accordingtohim,angiospermarose
240myainthePermianandtookaround140myabeforetheywidely
spreadinthecretaceous.InsimpleglossopterisscutumandOttokoria,
thefertilebranchcontainedabivalvescalehavingtwowingscalled
scutella.Thelattercarriedterminalovulesondichotomousgroupsof
branches.Foldingofthescutellaalongtheclusterofovulesformsthe
angiospermcondition.TheclosureconditionwasfoundinthePermian
fossilBreytenia.The3fertilebranchofLidgettoniacarries4-8disc-like
bearingseveralseeds.AgenusDenkaniadiscoveredfromRaniganj,
W.B.Indiabears6seedbearingcupulesthatareattachedtothelong
stalksbornefromthemidribofthefertilescale.Theleavesof
glossopterisarelanceolatewithreticulatevenation.Theconestructure
hasspirallyarrangedfertileleavesandformstheanthostrobilus.The
anthofasciculiui.e.leavesstructurewithtwofertilebranches,one
unableandotherisreportedinMudgea.Itiscomparablewiththe
angiospermflowerslikeRanunculusandAcacia.

24. 7.HerbaceousoriginHypothesis:Theancestralplantsarethoughttobe
consideredasrhizomatousherbsnotthetrees.DonoghueandDoyle
(1989)coinedthetermpaleoherbsforagroupofplantofMagnoliidae.
Theyfoundtooccurthefeatureslikeanomocyticstomata,twowhorlsof
perianthandtrimerousflowersintheplantsanditincludesthefamilies
likeLactoridaceae,Aristolochiaceae,cobombaceae,Piperales,
Nymphaceae&monocots.Accordingtothishypothesis,theancestral
plantspossessthefollowingfeatures-
Ancientangiospermplantswereperennialwithrhizomatousto
scramblinghabit,
Leavesweresimple,reticulateveinedanddichotomousbranchingof
secondaryveins,
Sieveelementswithtreacheryelementswithbothcircularborderedand
scalriformpittingwithobliqueendwalls,
Flowerswithracemoseorcymoseinflorescence,
Smallmonosulacatehadperforatetoreticulatesculpturing,

25. Carpelsfree,ovulesattachedproximallytotheclosure.Thereareoneto
twoorthotropus,bitegtmic,crassinucleateovuleandthedicotyledonous
embryo.
TherecentfindingssuggestthatGneopsidsaretheclosesttotheliving
relativesoftheangiospermsandtheclosestfossilgroupofthe
Bennettiales.AnthophytesduringtheLateJurassicdividedintostem
Angiophytes,theearlyangiospermsandcrownAngiophytes
constitutingtheextentgroupofangiosperms.
AgroupofProangiospermsCaytoniales,Zcekanowskialesand
DirhopalostachyceaewasidentifiesbyKrassilorintheJurassic.He
arguedtoconsidertheseplantsasangiosperminsteadofresearching
theirancestors.HefurthertracedLaurales-Rosalesseriesfrom
Caytoniales.Zcekanowskialespossessedbivalvecapsuleshaving
stigmaticbandsthatshowedlinkswithmonocots.
DirhopalostachyaceaeprobablyevolvedinHamamelidalesdueto
pairedovulesexposedonshield-likelateralappendages.

26. 6.Transitional-CombinationalTheory:J.Stuessay(2004)putforththis
theoryasfarastheoriginofangiospermisconcerned.Theangiosperms
evolvedgraduallyandslowlyfromseedfernsintheJurassic.Heconsiders
thatCarpels,doublefertilizationandtheflowerstoevolveoneafter
another.Thesethreefundamentaltransitionsmighthavetakenmorethan
100myatocompletetheprocess.Thefossilrecordconfirmedthatthe
livingangiospermdidnotcomeupuntilEarlycretaceouswhenthefinal
combinationofthesethreeimportantangiospermfeaturestookplace.The
theoryattemptstoremovediscrepancybetweenfossilandmolecular
phylogeneticdata.Thelattergivesindicationo0fPre-cretaceousoriginof
angiosperm.ButDNAsequencesshowedfirstchangewasincarpel
evolution.Theeventismuchearlierthanthefinalcombinationofallthe
threeangiospermfeatures.Thistheorygiveemphasisontheoriginof
angiospermfromseedfernsandnoothergymnospermshaddirect
phylogeneticlinktomodernangiosperm.
Itisacceptedthattheearlyangiospermsweresmalltreesorwoody
shrubswithsimpleevergreenentireandpinnatelyveinedleaveshaving
stipule.Furtheritisbelievedthatprimitiveangiospermsevolvedinvery
lateJurassicperiod.Thereare

27. Twoschoolsofthoughtregardingtheoriginofangiosperms.
TheEnglerianschoolconsidersCasurinaceaeasthemostprimitiveamong
dicotswhereasBesseyschoolthinksbisexualflowersofMagnoilialestobe
themostprimitive.Duringthelastfewyears,paleoherbsprovidethe
essentialclueonprimitiveangiosperm.
TheprimarybasalgroupswerechosenasprimitiveincludeCasuarinaceae,
Magnoliaceae,Winteraceae,DegeneriaceaeandCalcanthaceae.APGII
consideredMagnoliidaeandNympheidaeasthetruebasalgroupinsteadof
DegeneriaceaeandPlacedAmborellaceaeatthebeginning.
Attheendofthe20
th
century,theherbaceousoriginofangiospermshas
beengainingmuchmoreemphasisinthisregard.
Asfarastheoriginofmonocots,differenttheorieshavebeenputforward
bythenumberofscientistsasstatedbelow:
Bailey(1944)&Cheadle(1953)gaveemphasisonoriginofvesselsand
theyconcludedvesselshadindependentoriginandspecialinmonocotsand
dicots.
Cronquist(1968)didnotagreewiththeindependentoriginofvesselin
twogroups.

28. Hebelievedinaquaticoriginofmonocotsthatresemblewith
Nympheales.
Kjosakai,MoselyandCheadle(1970)didnotaccepttheviewof
Cronquist.AdvancevesselsareobservedinAlismatiaceaeinanaquatic
environmentandtheterrestrialmonocotsevolvedwithancientvessels
elementsinthemetaxylemofroots.
Monocotyledonsevolvedintwolines-OnefromRanunculoideaegiving
risetoAlismatialesandanotherfromheleboroideaegivingriseto
ButamalesasperHutchinson(1973).
Takhtajan(1980,1987)believedinacommonoriginofNymphealesand
Alismatialesfromhypotheticalterrestrialherbaceousgroupof
Magnoiliidae.
Dahlgrenetal.(1985)describedthatmonocotsevolved110myaago
duringEarlycretaceous.
Chaseetal.(1993)observedthemonophyleticoriginofandfromwithin
monosulcatepollenofMagonliidae.

29. References:
1. Google for images
Different websites for content,
Plant taxonomy-O.P.Sharma
Text Book of Plant Systematics-Chittaranjan Mohanty,
A Textbook of botany-Hait, Bhattacharyya & Ghosh
Advanced Plant taxonomy-A.K. Mondal
Disclaimer: This PPT has been prepared to enrich open source of
knowledge for the academic fraternity without any financial interest.