Floral syndrome and breeding system of endangered plant sinocalycanthus chinensis

Sinocalycanthus chinensis is a rare and endangered deciduous shrub endemic to Zhejiang, China. In order to understand the reproductive biology of S. chinensis and its possible effects to its status of being endangered, the floral syndrome and breeding system were investigated. A field investigation of the flowering course and functional floral morphology of Sinocalycanthus chinensis was conducted. Outcrossing index and pollen-ovule ratio, artificial pollination and bagging were used to measure the breeding system. The variation of morphology and quantity of different parts of flowers occurred commonly. Flowering lasted 7-9 days. During the flowering course, the stamen closed to the center gradually and finally surrounded the pistil. S. chinensis is a species of protogynous, the female organ mature before male organ and there is no obvious herkogamy. The flowering course for one flower of this species can be divided into six periods based on the flower morphology and gender function expression: Bud stage, Prophase of flowering, Female stage, Bisexual stage, Male stage, and Fade stage. The outcrossing index and pollen-ovule ratio of S. chinensis were 3 and 29571±5839, respectively. The results of pollination experiments showed that there is no apomixes, it is self-compatibility, and entomoplily playes a larger role in the process of pollination. These indicated that outcrossing is the main form in breeding system of S. chinensis and it is also self-compatibility. Thus S. chinensis appeares to have a mixed-mating system.