Abstract: Gymnocarpus przewalskii, a rare Tertiary relict species in the desert region of Central Asia, is a vital constructive species that constitutes the stony desert vegetation community, and its natural population is declining due to human interference. In the present study, based on field observations and artificial pollination experiments, we investigated the floral characteristics and breeding system of G. przewalskii, which are highly important for revealing its life history characteristics, discussing factors that affect the success of its reproduction, and developing conservation and management strategies. G. przewalskii is a plant with bisexual flowers that are small and apetalous. Each flower has 1 ovule and 10 stamens, with the 5 outerwhorl stamens being abortive. During anthesis, the flower has a small amount of nectar with strong unpleasant odor. During this period, there is a 46hour overlap between pollen viability and stigma receptivity and the incomplete female becomes mature first; in addition, the stigma does not come in contact with the anthers when the uniflorous florescence of most flowers ends. Thus, G. przewalskii flowers mainly exhibit herkogamy and adapt to crosspollination with a pollen/ovule (P/O) ratio of 1371.67 ± 236.21 and outcrossing coefficient of 3. Pollen from different sources (natural pollination, selfpollination, geitonogamy, and xenogamy) can all germinate on the stigma, but the growth rates of the pollen tubes vary. In geitonogamy and xenogamy, the pollen tubes grow faster, while in selfpollination, the growth is slowest, with growth ceasing in part of the pollen tube (43%) as it approaches the ovary, thereby it is not able to reach the ovule. The experimental results of artificial bagging show that G. przewalskii is apogamous and has few naturally born seeds, and the number of the seeds of naturally pollinated flowers is much lower than that of artificial xenogamous flowers, indicating the existence of pollination restriction caused by the insufficiency of crosspollinators. Partial protogyny and herkogamy in G. przewalskii are a floral mechanism adopted by the bisexual flowers to avoid the functional overlap of males and females and to promote outcrossing. The breeding system of G. przewalskii is facultatively xenogamous and it requires pollinators. The success of its sexual reproduction is mainly affected by two factors, partial selfincompatibility and pollination restriction.

Key words: sampling scale, secondary forest., spatial distribution, species diversity index