Floral traits and pollination system of Zygophyllum xanthoxylum in the managed and wild populations in an arid region of Northwest China

Zygophyllum xanthoxylum, which belongs to Sarcozygium of Zygophyllaceae, is one of the ecologically important species in Northwest China. In order to understand the pollination system of Z. xanthoxylum, we investigated the following characteristics of this species in the Urat Desert-grassland Research Station in western Inner Mongolia of China: flowering dynamics, pollen viability, pollen limitation, floral visitors and breeding system. The results showed that the flowering period and flowering peak were different between the wild and managed populations, being longer in the managed population. Z. xanthoxylum was pollen-limited, and pollen limitation was more intense in the wild population than in the managed population. Chalicodoma deserticola(Hymenoptera) was found to be the most frequent pollinator in the wild population, while Anthophora fulvitarsis(Hymenoptera) was the most frequent and effective visitor in the managed population. Out-crossing was dominant in the breeding system and self-pollination just played an assistant role to assure the reproduction of Z. xanthoxylum.