耳草属(HedyotisL.)的起源及地理分布

依据耳草属的系统学，古地理学和细胞染色体资料分析和推论，耳草属植物的起源地点在冈瓦纳古陆，很可能在古陆辽阔的东北部地区。耳草属植物的起源时间不应晚于侏罗纪，有可能在三叠纪就已经出现，并在侏罗纪得到广泛的传播，其迁移的路线有四条，即从起源中心向东经上耳其，伊朗进入东南亚地区，向东南通过古南大陆向印度板块和徜大利亚扩散，向北进入北美地区，向西南进入南美洲地区,随着冈瓦纳古陆的分离，印度板块向北漂移以及澳大利亚与古南大陆的分离，植物迁移与扩散的速度受到了制约，耳草属植物现代分布格局形成的原因在于传播途径的隔断和第四纪冰川的作用。

THE ORIGIN AND DISTRIBUTION ON GENUS HEDYOTIS L.

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.