XVI International Botanical Congess
Phylogenetic relationships among 19 taxa of Weigela and Diervilla were inferred from ITS sequences of nuclear rDNA. The ITS phylogenies did not support the monophyly of Weigela and favored the taxonomic hypothesis proposed by Nakai who recognized four distinct evolutionary lines (Diervilla, Macrodiervilla, Weigelastrum, and Weigela). However, recognition of the two sections, Calysphyrum and Weigela was not supported. The hybrid origin of the species from the putative parents, W. florida and W. subsessilis, was not supported. Substantial morphological differences between Diervilla and W. middendorffiana do not support the morphological stasis concept. The paraphyly of Weigela and the rapid morphological evolution between the W. middendorffiana and Diervilla indicate the importance of phylogenetic studies of other 'disjunct genera'.