Speciation and taxonomy of the endemic family Aucubaceae in Sino-Japanese floristic region

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Aucuba, the only genus in the family Aucubaceae, is endemic to the Sino-Japanese floristic region, and is diversified around southwestern China. In the genus 10 to 20 dioecious evergreen shrub or tree species were recognized, but there are taxonomic confusions because of quite variable characters. For the chromosome numbers, it is thought that A. japonica was the only polyploid complex in the genus. Our previous study based on chloroplast phylogeny indicated that tetraploidization occurred independently at least three times within A. japonica. It is possible that other species in China might include polyploids. In the present study, (1) to evaluate the chromosomal evolution, (2) to understand the speciation process of A. japonica, (3) to revise the classification of the genus , we conducted the phylogenetic analysis based on additional sequences of chloroplast DNA noncoding regions and nuclear DNA (ITS region and exon of GapC gene) and the flow cytometric analysis for several species obtained from China and its neighboring regions. Our results indicate that 1) the genus is divided into two lineages of shrub having dark purple flowers and tall-species having pale yellow flowers, 2) the traditional recognition of A. chinensis has been misinterpreted, and 3) several species were polyploids and most of them, including A. japonica, were originated by allopolyploidizatios