Observation of male flowers and induced fruit production of tropical seagrass Syringodium isoetifolium (Alismatales: Cymodoceaceae) in an ex situ aquarium

Sexual reproduction is essential for enhancing the genetic diversity of seagrasses, allowing these clonal organisms to be more adaptive and resistant to disturbances. However, the flowering and fruiting characteristics of tropical seagrass species remain largely unknown, with limited phenological information widely available and described. The male flowers of Syringodium isoetifolium were identified 26 days after cyme inflorescence was observed, while the first female flowers were identified 11 days after the males were identified. A total of 14 male and 6 female flowers from 5 male and 3 female flowering shoots were identified during the fruiting period from April to July 2025, resulting in a 3:5 female to male flower sex ratio. All six female flowers were artificially pollinated using the available pollen, and two fruits were observed after three days. The fruiting plants exhibited a reduction and loss of belowground biomass 34 days after fruiting was observed. The documentation of tropical seagrass flowering and fruiting can provide vital information for field monitoring and seagrass phenology research. The successful pollination observed in this ex situ study suggests the potential value of intervention in enhancing fruiting success. However, due to the observational nature of this study in ex situ and semicontrolled conditions, these preliminary observations are not conclusive but may have implications for S. isoetifolium reproductive ecology.