世界杨柳科植物的起源、分化和地理分布

ORIGIN, DIVERGENCE AND GEOGRAPHICAL DISTRIBUTION OF SALICACEAE

全世界杨柳科共有６５０种。分为３属，即钻天柳属、杨属和柳属。花序下垂利于风媒，花序直立利于虫媒。钻天柳属具有利于风媒的雄花序和利于虫媒的雌花序，这是一种进化不完全的现象，是杨柳科中最原始的类群；杨属是杨柳科中适应风媒的分支；柳属是适应虫媒的分支。绝大多数种类分布在北半球温带，是较典型的温带科。其现代分布中心和分化中心在东亚地区。根据地史资料、化石资料以及杨柳科和其外类群的现代分布情况，我们认为，杨柳科起源于东亚区东北部，即我国东北及日本和朝鲜一带；其虫媒分支和风媒分支的形成时间不晚于早白垩纪晚期，而这两大分支形成前的先锋类群很可能在早白垩纪以前就已经出现。

Salicaceae consists of 650 species in the world and is divided into 3 genera,Chosenia Nakai, Populus L。and Salix L。 The pendulous catkin is favourable to wind pollination and the erect catkin is favourable to insect pollination。 The genus Chosenia has staminate catkins that fa-vourable to wind pollination and pistillate catkins that favourable to insect pollination。This kind of structure of the genus Chosenia is an incomplete evolution phenomenon。So, Chosenia is the most primitive genus of the family.Populus is branch of wind pollination and Salix is an other branch of insect pollination。Most species of the family is distributed in north hemisphere It is a typical temperate family。 The centre of its modern distribution and diversity is in east Asia。 The place of origin of the family is in the northeast part of East Asia, According to the data of histori-cal geology and fossils,and modern distributon of the family and its outer group,the date of the origin of the family′s two branches(wind pollination and insect pollination)is not late in the Aptian of Early Cretaceous, and the ancestors before the origin of the two branches maybe pressent before Early Cretaceous