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3010Frequencyandspeciesabundance
19
Pondweedsconstitutedalmosthalfofallvascularplants(21species)and
included19Potamogetonand2Stuckeniaspecies0Thefrequencyofeachspecies
inthesegroupswaslowinthetotalnumberofsamplesanddidnotexceed
5%,e0g0Potamogetonobtusifolius(303%),Stuckeniapectinata(301%),P
.natans
(200%),P
.friesii(107%),P
.perfoliatus(107%),P
.gramineus(102%),P
.praelongus
(100%)0P
.acutifolius,P
.alpinus,P
.rutilus,P
.pusillus,P
.polygonifoliusandP
.an-
gustifoliuswereevenlesscommon(Table2)0
Stoneworts(Charales)wereyetanotherplantgroupwhich,incompari-
sonwithvascularplantsandmosses,waslessnumerous(17;frequent1903%
ofthetotalofspecies)andoccurredin3713samples(35%)0Nitellaflexilis
(907%,1027samples)wasmostoftenrecorded,whileCharadelicatula(807%),
C.globularis(807%),C.tomentosa(500%),Nitellopsisobtusa(306%),C.rudis(302%),
C.contraria(301%),C.aspera(200%)andN.opaca(105%)werefoundlessfre-
quently0Thefrequencyoftheremainingspeciesdidnotexceed1%(Table3)0
Theanalysisofthepercentageofwinter-diapausingplantsandnon-
diapausingoneswasasourceofinterestinginformation0Evergreenspecies
(withoutwinterdiapause)occurredwithaveryhighfrequencyof8308%
(8884sampleswithsubmergedplants),althoughthemeannumberofspecies
frombothgroupswasverysimilarinthesamples(1064and1056species/001m2,
respectively)0
Thefrequencyofindividualspeciesinthedepthzonesofthelakeswas
different0Itwasvaried(Table2andTable3)andamountedto5003±2401%
(Me=4604%)onaverage0However,only14speciesoccurredveryfrequently
(>50%),whichmeansthatthe70remainingunderwaterspecieswereless
common0Inthenorth-westofPoland,Sphagnumdenticulatum(7105±3403%;
Me=90;261depthzones),Isoëteslacustris(6406±3402%;179),Littorellauni-
flora(5808±3208%;68),Lobeliadortmanna(5803±3409%;130),Charadelicatula
(5700±3507%;129),Warnstorfiaexannulata(5209±3205%;186),Myriophyllumal-
terniflorum(5007±3107%;223)andSphagnumcuspidatum(5007±2900%;77)oc-
curredwithhighfrequency0
Specieswhichwereveryrareinthelakesandhadlowfrequencyinthe
totaloftheplantsampleswerealsocharacterisedbyhighfrequencyindepth
zones0Theoccurrenceofthesespecieswasconnectedwithasmallgroup
ofwaterbodies,wheretheyoccupiedonlysomedepthzones,forexample:
Najasminor(frequency5609±3504%,in3lakes,8zonesintotal),Utriculariain-
termedia(8303±0%,in2lakes,2zones),Potamogetonpolygonifolius(7607±808%;
in2lakes,3zones)andSphagnumriparium(6107±2604%,in5lakes,6zones)0
