Flowering characteristics and breeding system of <italic>Helleborus foetidus</italic>

Aims: This study investigated the flowering process and breeding system of Helleborus foetidus to provide a theoretical basis for the development of stress-resistant germplasm resources and the selection of new varieties. Methods: Through observations of flowering phenology, floral characteristics, assessments of pollen viability and stigma receptivity, pollen-ovule ratio (P/O), outcrossing index (OCI), and artificial pollination experiments. Results: The results showed that: the flowering period of Helleborus foetidus populations lasts from November to the end of March, with a single plant flowering for approximately 119 days and a single flower lasting 37–45 days. Pollen viability tests indicated that the acetocarmine staining method was ineffective, while the TTC staining method showed 77.43% viability, and the in vitro germination method reached 94.47%. Stigma receptivity was strongest during the peak flowering period. The P/O ratio was 15 470, and the OCI value was 3. The fruit set rates for self-pollination, geitonogamy, xenogamy, natural pollination, and emasculation with bagging were 62.86%, 77.14%, 88.57%, 97.14%, and 0, respectively. Helleborus foetidus exhibits a facultative outcrossing breeding system, relies on autonomous self-pollination to ensure reproduction, and does not exhibit apomixis. This species exhibits high flower production, a long flowering period, and strong self-seeding capability, demonstrating promising potential for the breeding of shade-tolerant ornamental plants and the exploration of stress-resistant genetic resources. Conclusion: The findings of this study provide both a theoretical and material foundation for developing new Helleborus varieties with strong adaptability and high ornamental value. Future research may further investigate the molecular regulatory mechanisms and key genes involved in its facultative outcrossing behavior.