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热带亚热带植物学报 2001
THE ORIGIN AND DISTRIBUTION ON GENUS HEDYOTIS L.
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Abstract:
As oneof thelargestandpantropicalgenerain thefamilyRubiaceae,thegenusHedyotis L.sensulato,includingsubgeneraHedyotis,Oldenlandia andHoustonia,is appliedin thispaper.They characterizedbyhavingtetramerousflowerswithvalvatecorollasandequalcalyxlobes,expanded,fleshy,peltateplacentaeand moderatelyflattenedcapsularwithsclerifiedendocarps.Basingon the extant literatures,699speciesareincludedinthisgenus.TropicalAfricaandAsiaaretwomoderndistribution centers.Endemicspeciesaredistributedinalltropicalcontinents.About68species(includingvarieties)growingin S.and SW China.The moderndistributionpatternand cytogeographydatarevealthat:(1)Hedyotis was originatedin theGondwanalandbeforelateJurassic,andmightbe originatedon the ampleareaof NEGondwanalandduringJurassic,eveninearlyTriassic;(2)Theydispersedinfourways fromtheoriginalcenter:eastward,to SE AsiaviaTurkey,IranandS.China,wherewasthesouthern areasof theLaurasialand;southeastward,to IndiaandAustraliaviapaleo-antarcticland;northward,to NorthAmericaviacentralpaleo-pacific;southwestward,to S.America,whichwasunitedwithAfricaat thattimeandwasalsoonemainpartof theGondwanaland.Thecontinentaldrift,especiallythebreakup of Gondwana,sloweddownthespeedof suchdispersalin Jurassictime.Subsequently,thespecies developedin theseseparatedcontinents.The globalglacierhadalsoplayedan importantrolein the presentdistributionpattern.
