Intrageneric relationships of maple trees based on the chloroplast DNA restriction fragment length polymorphisms

A maple tree genus,Acer is the largest genus in broad-leaved deciduous trees and contains about 200 species. A delimitation of the genus is clear but the intrageneric classification was controversial because of homoplasies in morphological characters. In this study, a phylogenetic relationship inAcer was inferred based on chloroplast DNA restriction site polymorphisms with 17 restriction endonucleases and previously proposed intrageneric classifications were evaluated. The phylogenetic tree showed that (1) sectionsArguta, Cissifolia, Lithocarpa, Macrantha, Palmata, Spicata, Tataricum, Trifoliata sensu Ogata (1967: Bull. Tokyo Univ. Forests 63: 89–206) were monophyletic groups respectively, (2) sectionsCampestria, Goniocarpa, Platanoidea sensu Ogata (1967) were polyphyletic respectively, and (3) sectionsDistyla andParviflora formed a sister group. An average of estimated nucleotide substitution rates of Acer chloroplast DNA was calculated as 7.9×10⁻¹¹±1.4×10⁻¹¹ nucleotide substitutions par site par year, which coincides well with previously reported rates of perennial plants. Divergence eras of eastern Asia and North American species in both sectionsSpicata andRubra were estimated to be late Miocene. In consideration with previous data, multiple migrations and disjunctions are likely to have formed the eastern Asian and North American disjunct distribution.