MARSILEA notes in detail for II year Botany.ppt

II BSc IVth SEMESTER

1. MARSILEA

2. SYSTEMATIC POSITION
Division Filicophyta
Class Leptosporangiopsida
Order Marsileales
Family Marsileaceae
Genus Marsilea.

4. Characteristic features
Thisorderincludesasinglefamily,Marsileaceae.
Thefamilyincludesthelivinggenera-Marsilea,Pilularia
andRegnellidium.
Theyareheterosporousaquaticferns.
Thesporangiaoftheseareproducedwithinspecial
structuresknownassporocarps.
Eachsporocarppossessesmanysoriwhichbear
microsporangiaandmegasporangia.
Thesoriaregradate,i.e.,theoldestsoriarefoundattheir
terminalendofthereceptacleandyoungestatthebase.

5. Thereareabout65speciesofMarsilea
distributedallovertheworld.
Theyaremorecommonlyfoundintropical
regions,suchas,AfricaandAustralia.
Theyarehydrophyticoramphibiousplants.
Theygrowrootedinthemudofmarshesand
shallowpools.
AsingleplantofM.vestitamaygrowinall
directionsuntilitcoversanareatwenty-five
metresormoreindiameter.

6. InM.vestitaandmostofotherspeciesthe
sporocarpsdeveloptomaturityonlyontheplants
thatarenotsubmerged.
M.minutaandsomeotherspeciesproduce
sporocarpsintheaquatichabitat;ontheotherhand
M.aegyptiacaneverproducesthesporocarpsinthe
aquatichabitat.
AnAustralianspeciesM.hirsutacansurviveindry
conditionsthroughouttheyear.

7. ExternalMorphology:
Stem:
ThespeciesofMarsileapossessarhizomewhichcreepsonorjust
beneaththesurfaceofthesoil.
Therhizomeisslender,branchedandpossessesnodesand
internodes.
Theleavesarebornealternatelyalongtheuppersideoftherhizome
usuallyatthenodes.
Oneormoreadventitiousrootscomeoutfromeachnodeonthe
undersideoftherhizome.
Therhizomeisdichotomouslybranchedandiscapableofindefinite
growthinalldirectionsandcoversanareamorethantwenty-five
metresindiameter.

8. Leaves:
Theleavesarebornealternatelyalongtheuppersideofthe
rhizomeatthenodes.
Theleavespossesscircinatevernationtypicalofmost
Filicales(ferns).TheyoungpartsoftheleavesofM.minuta
andothersarecoveredwithnumerousmulticellularhairs.
Theleavesofsubmergedplantspossesslongflexible
petiolesandleaflaminathatfloatonthewatersurface.
Whentheplantsgrowonmudormarshyplacestheleaves
havegotshorterandthepetioleserectandstouterwhich
spreadtheleavesintheair.

9. Theveinsofeachpinnaaredichotomously
branchedandhavenumerouscrossconnections
resultinginclosereticulumofveins.
Theshapeofpinnaevariesfromobovateto
obcuneate.Themarginalsovariesfromentireto
crenate,e.g.,M.minutaorfromcrenatetolobed
asinM.aegyptiacaaxerophyticform.
Atnightthepinnaeofaerialleavesbecomefolded
upwardsandexhibitthesleepingmovement.

10. Thesporocarpsareborneonshortpedunclesnearthe
baseofthepetiole.
Inmajorityofcasesthepeduncleorstalkofthe
sporocarpisunbranchedandbearsasingle
sporocarpatitsapex.
Marsileaquadrifoliapossesses dichotomously
branchedpeduncle,whichbearstwotofive
sporocarps.
InM.polycarpasingledichotomouslybranched
pedunclebearsabout6to26sporocarps.

11. Roots
Oneormoreadventitiousrootsareborneateach
nodeontheundersideoftherhizome.
Theadventitiousrootsmayariseevenfrom
internodes,e.g.,inM.aegyptiaca.
InM.minutatherootsmaydeveloplaterally.
TherootsofM.minutasecretecarbonicacidand
becauseofthissecretiontherootscouldpenetrate
theshellsofpondsnails.

12. Anatomy
Rhizome
TherhizomeofMarseliapossessesanamphiphloicsiphonostelic
vascularcylinder.
Theoutermostlayeristhesingle-layeredepidermiswithoutany
stomata.
Thecortexisdifferentiatedintoouterandinnercorticalregions.The
outercorticalregionconsistsofcompactparenchymatoustissue.
Thisregionmaybeonetoseveralcelledinthickness.Justbeneath
thisthecorticalregioncontainslargelacunaeorairspaces
(aerenchyma).
Thelacunaeareseparatedfromeachotherbyonelayered
parenchymatoussepta.

13. Thisregionmaybeconsideredthemiddlecortex.
Internaltothisregiontheinnercortexisfound.
Thisconsistsofascleroticzone.Thecellsconsisting
thisregionarethick-walledsclerenchymatouscells
(fibres).
Beneaththisregionthecortexagainconsistsof
compactparenchymatoustissueactingasstorage
tissuecontainingstarchinthem.Someofthetannin
cellsmaybefoundinthisinnermostregion.

15. Petiole
Theinternalstructureofapetioletransverse
sectionisasfollows-
Theoutermostlayerissingle-layeredepidermis.
Justbeneaththeepidermisthereishypodermal
layer.
Thenthereisothercortexconstitutingoflargeair
spacesorlacunae(aerenchyma)separatedfrom
eachotherbysepta.

16. Theinnercortexiscomposed ofcompact
parenchymatouscells.
Inthisregionsomeofthetannincellsmaybepresenthere
andthere.Inthecentralregionofthepetiolethereisstele
whichismoreorlesstriangularinoutline.
Thesteleissurroundedbyasingle-layeredendodermis.
ItpossessesV-shapedmassofxylemwiththeexarch
protoxylem.
ThetwoarmsofVarequiteseparateandsomewhat
curvedfromeachother.

18. Root
Inthetransversesectionoftheroot,theepidermis,
cortexandstelemaybeseen.
Theepidermisissinglelayeredandcomposedofthin-
walledparenchymatouscells.
Thecortexoftherootisdifferentiatedintotwo
regions.
Theouterregionconsistsoflargeairspacesor
lacunaeseparatedbyseptafromeachothertheinner
zoneofthecortexconsistsofafewlayersofsclerotic
cells.

19. Innertothecortexthereissinglelayered
endodermis.
Justbeneaththeendodermisthereissingle-
layeredpericycle.
Inthecentreofthestelethereistypical
diarchandexarchstructurewithadiametric
platelikestrandofxylem.
Thephloembandsarefoundoneithersideof
thexylemplate.

21. Reproduction:
ThereproductioninMarsileatakesplacebyvegetativeand
sexualmethods.
Vegetativepropagation
Thevegetativereproductiontakesplacebymeansof
speciallydevelopedstructuresknownastubers.
Inthedryconditionscertainbranchesdevelopfromthe
rhizome,whichswellbecauseofthestorageoffood
material,andaretermedastubers.
Thesetuberssurviveintheunfavourableanddrought
conditions,andonthereturnoffavourableconditionsthey
germinateintonewplants,e.g.,M.hirsuta.

22. Sexualreproduction
Theplantisasporophyte.
Itbearsthespecialstructuresknownassporocarps
whichcontainmicroandmegasporangiainthem.
Itisheterosporous.Thesporocarpsareborneonshort
pedunclesabovethebaseofthepetiole.
Inmostcasesthepeduncleisunbranchedandbearsa
singlesporocarpatitsapex.
InM.quadrifoliathepeduncleisdichotomously
branchedandbears2to5sporocarps.

25. Thesporocarpsmaybeovalorbean-shaped.
Intheearlierstagesofitsdevelopmentitis
softandgreenbutlateronitbecomes
sufficientlyhardandbrownincolour.
Suchprotuberancesconsistofoneortwo
teethandraphe.

26. Therapheisfoundlaterallyfusedtobaseof
thesporocarpattheendofthepeduncle.
Beyondtheraphetwoteethorprojectionsare
found.Theseteethareunequalinsize.
Thelowertoothisstouterthantheupperone.
Insomespeciestheteethareveryprominent.

27. Areceptacledevelopsattheregionwhere
eachlateralveinforksdichotomously.
Thereceptaclesofonevalvealternatewith
thoseontheoppositevalveofthesporocarp.
Aflap-likeoutgrowthtwo-celledthickextends
likeahoodovertheentirereceptacle.
Eachreceptacleprojectsinwardfromthewall
ofthesporocarp.

28. Life Cycle ofMarsilea:
MatureplantofMarsileaisdiploid.
Marsileaisaheterosporousfernbecauseitproduces2
differenttypesofsporesi.e.,microsporesand
megaspores.
Micro-andmegasporemothercellsareproducedinside
micro-andmegasporangiumrespectivelywhichrepresents
thelatestageofsporophyticgeneration.
Afterreductiondivisionmicrosporesandmegasporesare
producedwhichrepresenttheinitialstageofgametophytic
generation.

29. Microsporegivesrisetomalegametophytewhich,in
turn,producesarchegoniumandegg.
Bothantherozoidandeggfusetofromadiploid
oospore(2x).
Theoosporeistheinitialstatesofsporophytic
generation.Hence,inthewaythesporpyticand
gametophyticgenerationalternatewitheachother
althoughthesporophyticphaseisdominantover
gametophyticphase