耳草属(HedyotisL.)的起源及地理分布

THE ORIGIN AND DISTRIBUTION ON GENUS HEDYOTIS L.

摘要:

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土耳其、伊朗进入东南亚地区,向东南通过古南大陆向印度板块和澳大利亚扩散,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。

Abstract:

As oneofthelargest andpantropical generainthefamily Rubiaceae，the genus Heddyotis L．sensu lato， including subgenera Hedyotis，Oldenlandia and Houstonla，is applied in this paper．They characterized by having tetramerous flowers with valvate corollas and equal calyx lobes，expanded，fleshy，peltate placentae and moderately flattened capsular with selerified endocarps． Basing on the extant literatures，699 species are included in this genus．Tropical Africa and Asia are two modern distribution centers．Endemic species are distributed in all tropical continents．About 68 species(including varieties) growing in S．and SW China．The modern distribution pattern and cytogeography data reveal that：(1)Hedyotis was originated in the Gondwana land before late Jurassic，and might be originated on the amplearea of NE Gondwana land during Jurassic，even in early Triassic;(2) They dispersed in four ways from the original center：eastward，to SE Asin via Turkey，Iran and S．China，where was the southern areas of the Laurasia land; southeastward，to India and Australia via paleo-antaletie land：northward，to North America via cent1al paleo-pacifie; southwestward，to S．America，which was united with Africa at that time and was also one main part of the Gondwana land．The continantal drift，especially the breakup of Gondwana， slowed down the speed of such dispersal in Jurassic time．Subsequently， the species developed in these separated continents．The global glacier had also ptayed an important role in the present distribution pattern．