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.