Abstract: Flowering and breeding characteristics are important for understanding plant population reproduction. In this paper, the flowering dynamics and breeding system of Mirabilis jalapa L. were studied by using the data of pollen－ovule ratio (P/O), pistil recipient phase, out-crossing index (OCI), pollen viability, numbers of pollen grains and their germination ratio on stigma, and emasculation. The results showed that the flowering period of M. jalapa was about four months (from June to October), and the life span of individual flower was generally 2-3 days. For each flower, the flowering process could be divided into five periods, i.e., pre－dehiscence, initial dehiscence, full dehiscence, perianth closure, and withering, based on the changes in floral morphology and anther dehiscence. In the period of perianth closure, the percentage of stigma inside of closed perianth was 66.80% when it was sunny, 81.65% when it was cloudy, and 99.22% when it was rainy. The floral diameter was 22-28 mm. In the majority of M. jalapa, there was a temporal isolation between male and female organs within the same flower, i.e., the gynoecium ripened early, stigmas and anthers were arranged at the same height, and the outcrossing index (OCI) was 3. However, in a lesser percentage of flowers, there were temporal and spatial isolations betweenmale and female organs within each flower. The gynoecium ripened early, with an out-crossing index (OCI) of 4. According to the criteria put forward by Dafni, most of M. jalapa individuals had the breeding system of self－compatible and only requiring pollinators sometimes, and fewer were of outcrossing, partially self-compatible, and requiring pollinators. The pollen－ovule ratio (P/O) was approximately 269. Based on Cruden’s criterion, the breeding system could be termed as facultative autogamy. For about 6 hours after flowering, when stigmas were at the highest receptivity, 56.29% of the pollen was viable. According to the results of emasculation, bagging, and artificial pollination, there was no agamospermy, and the breeding system of M. jalapa was determined to be largely self-compatible, and only requiring pollinators sometimes. M. jalapa preserved a high percentage of stigma inside of closed perianth, which could be regarded as an adaptive strategy for reproduction under unfavorable environmental conditions.

Key words: Tree ring, Climate change, Changbai Mountain