基于细胞核rDNA ITS片段的水青冈属的分子系统发育

对山毛榉科水青冈属6种、1亚种、1栽培变种的ITS区片段进行了测序和分析，并对其中2个具有ITS序列多态性的分类群进行了ITS区克隆。水青冈属ITS系统发育树聚成两支，位于基部的是分布于北美的大叶水青冈，另一分支则包括了欧洲和东亚的类群。在欧洲和东亚分支中，又包括两支，其中日本北部的波叶水青冈位于基部，台湾水青冈和欧亚大陆的水青冈形成另外一支。ITS区分析与现行的水青冈属基于形态学性状的属下分类系统有一定差异，而与本属现存物种的地理分布格局较为一致。各类群间TIS区序列差异较小，显示属内现存物种的分化时间不是太长。

Molecular Phylogenetic Inference in Fagus (Fagaceae) Based on ITS (Internal Transcribed Spacer) Sequence of Nuclear Ribosomal DNA

The nrDNA ITS sequences of 6 species,1 subspecies and 1 cultivated variety of Fagus were attained and analyzed.Of them,two taxa with polymorphic ITS sequences were identified and cloned.The most parsimony phylogenetic tree revealed two divergent clades existed.In one clade,the two cloned accessions of North American F.grandifolia appeared in the basal position of the tree.In another clade,the European and East Asian species included.The Japan F.crenata was relatively basal and sister to other two branches -- the two cloned accessions of F.hayatae subsp.hayatae (a subspecies endemic to Taiwan) which formed a branch,while the Eurasian taxa ,F.sylvatica,F.sylvatica cv.Purpurea,F.longipetiolata,F.hayatae subsp.pashanica and F.engleriana formed another branch.Result did not support the current Fagus infrageneric system based on morphological characters,nevertheless,very coincided with the genus's distribution pattern.Since only a few variations of ITS sequences were found in the sequence alignment,speciation process of the extant Fagus may be occurred not too early.