To explore the biosystematics of the Calligonum mongolicum complex (Polygonaceae), the flowering phenological period, breeding and pollination characters and seed set of the complex (Calligonum Mongolicum Turze, Calligonum chinense A. Los., Calligonum gobicum A. Los., Calligonum pumilum A. Los. and Calligonum zaidamense A. Los.) were documented in the Turpan Eremophyte Botanical Garden, China. The sequences of the nuclear ribosomal ITS and ETS region were employed to differentiate the Calligonum mongolicum complex and other species in sect. Medusae. The results showed species of the Calligonum mongolicum complex occupied overlapping flowering periods and had consistent pollination agents. Their breeding systems are all self-compatible, tend to be out-crossing and they interbreed amongst each other (out-crossing index, OCI = 4).The crosses within and amongst species had high seed sets (44 - 65%). Phylogenetic analyses of Calligonum sect. Medusae and the network analysis of nrDNA (ITS and ETS) in the complex suggest interbreeding amongst "species" within the complex and provide evidence for taxonomically merging the five species in the complex. The detected hybridisation, occurring within the complex, suggests the need to improve traditional methods of ex situ plant conservation in botanical gardens for maintaining genetic diversity of Calligonum within and amongst species from different geographic areas.
