论三白草科的系统演化和地理分布

ON THE EVOLUTION AND DISTRIBUTION IN SAURURACEAE

根据细胞学、孢粉学、花器官发生和发育、花部维管结构、胚胎学、比较形态及解剖学等方面的证据，对三白草科４属６种的系统演化关系进行了详细论证。并联系古地理、古气候和古植物的有关史料对三白草科分布区的起源作了据理推论。三白草科大约起源于早白垩纪古北大陆东南部。它的原始类型可能与现代三白草属的形态大体相似，为一种多年生具根状茎的草本，花小、无被、具苞片。白垩纪末期三白草的原始类群已完成它在古北大陆的迁移和扩散，参与了南劳亚统一植物区系的组成。早第三纪以后在东亚和北美分别形成了两个分化中心。由于三白草科为喜温湿的亚热带类群，因而第四纪冰川之后，它在欧洲和西亚的成员灭绝，从而形成了东亚─北美间断分布的格局。东亚现存四分之三的属并代表着科内从原始到进化的各个阶段，是三白草科多样化中心和可能的起源地。

Saururaceae is a small relict family distributed disjunctly between Eastern Asia and North America。 At the present time it only contains 4 genera and 6 species. According to the com- prehensive analysis of the data from cytology, palynology, floral organogenesis and vasculature,embryology,comparative morphology and anatomy,the phylogenetic relationship among the genera of Saururaceae are inferred. The primitive genus Saururus with 2 species is considered much more primitive than the other three genera because it has preserved the probably most prim-itive characters from their ancester. Another Asian genus Gymnotheca with 2 species presents transitional group in the family. Anemopsis is a specialized genus,which is adaptable to the alka-line seasonal xeric place。 Houttuynia is the most advanced taxon in Saururaceae,because it has much more derived characters。Combined the phylogenetic data with the information of palaeogeography,palaeoclimate and fossil record, the origin and formation of distribution of Saururaeeae are discussed。saururaceae is probably originated at the very early Cretaceous period. At that time,Laurasia was still a completed continent and Gondwana land just started to break.The primitive form of Saururaceae may concentrated in south region of Laurasia。The ancestral saururaceae is probalbly similar to the form of nowadays Saururs,a kind of small, rhizomatous perennial herb,with simple flower subtended with bract.During the Cretaceous the climate of southern Laurasia was humid subtropical in general.The primitive genus Saururus thus already completed its disinte-gration and migration in Southern Laurasia,and was belonging to the Late Cretaceous and Early Terliary palaeotropical flora in Laurasia Tethys segregated the way passing to Gondwana。Since Tertiary up to Early Quaternary two differentiation centres developed in Eastern Asia and North America respectively。The modern distribution patterns may be developed as the re-sults of the climate change after the Tertiary Himalayan orogeni movement and the consequence of glacial period during the Late Tertiary and Quaternary. The members of Saururaceae plants become extincted in most parts of Eurasia and North America,but in Eastern Asia and Southeastern America the glaciation was much less heavier,the mesophytic plants were survived in some refugees. At present 75% of total genera and 67% of total species have been collected from Eastern Asia。Obviously this region is the diversifeation and probably origination centres of the family Saururaceae