Karyomorphology of Heptacodium (Caprifoliaceae s.str.) and its phylogenetic implications

A karyomorphological study of the species Heptacodium miconioides and five species in Caprifoliaceae of presumably related genera [Abelia and Depelta (Linnaeeae); Lycesteria and Lonicera (Caprifolieae); Weigela (Diervilleae)] reveals similarities in some karyological features such as structure of interphase nuclei, chromosome size, and condensation behaviour of chromosomes during mitotic prophase. However, differences between them in chromosome base number and morphology of metaphase chromosomes have also been revealed. The chromosome number of Heptacodium 2n = 28 is unique in Caprifoliaceae, presumably having resulted from polyploidization following hybridization between two ancestral species (possibly with chromosome base number x = 8 or 9) bearing characters of tribes Caprifolieae and Linnaeeae, respectively. The phylogenetic position of Heptacodium is discussed based on combination of karyomorphology and previous morphological and molecular data.