Abstract: Scutellaria tsinyunensis is an endangered plant species endemic to Jinyun Mountain in Chongqing, China. This paper focuses on the floral biology and breeding system of S.tsinyunensis by using yield observation, stigma receptivity test, pollen-ovule ratio, out-crossing index, and fruit set under a serious pollination treatments. The results show that the floral display and floral design of S.tsinyunensis have a type of pollination syndrome fit for insects without nectary, Bombus and Syrphidae are the main pollinators. P/O ratios were 7 618±390, indicated that the breeding system was xenogamy. S.tsinyunensis is a self-incompatibility species demonstrated by the pollen transfer experiments. Besides the sexual interference and lower pollen viability and stigma receptivity, the limit of climate to pollination and no enough pollinator visiting contribute to the lower percentage of fruit setting, which is only about 20.08%. Considered the lower fruit set number (about 5.6/plant) and lower percentage of seed germination (only about 3%), the lower ability of reproduction may be the direct reason for the endangered status of S.tsinyunensis.

Key words: Scutellaria tsinyunensis, floral biology, breeding systems, endangered mechanism