A morphometric study of Chinese Rubia sect.Oligoneura (Rubiaceae: Rubieae)
Rubia is the type genus of Rubiaceae, comprising ca.80 species.China is an important diversity center for Rubia with approximately half of its species, most of which belong to sect.Oligoneura.The morphological variations and taxonomy are complicated in sect.Oligoneura.To provide some statistic evidences for the classification of sect.Oligoneura, we explored a morphometric study based on 20 species (171 specimens) from the section using 28 qualitative and three quantitative characters.Our results showed that the principal components analysis produced the similar result as the cluster analysis, though the accumulation rising slowly with the first three principal components with only 48.56% of the total variations.Contributions to the first three components included leaf shape(leaf length/leaf width), length of leaf petiole, leaf veins, number of leaves in each whorl, and life forms, which were also important to traditional classification of the genus.Our results are congruent with molecular phylogenetic results and support the recognition of ser.Chinensis, R.mandersii group, R.angustissima group and R.siamensis group, but not ser.Cordifoliae.Our results also indicate that most species in sect.Oligoneura can be well distinguished.Therefore, our study suggests that morphometric analysis provides good evidences for species identification and classification within sect.Oligoneura as well as for the whole genus.