Coffea arabica, C. canephora, and C. liberica’s coexistence in one location or proximity areas could promote interspecific pollination. However, information related to floral phenology and flower structure of these three coffee species is insufficient. This research aimed to identify the divergence of flowering phenology and flower morphometrics among C. arabica, C. canephora, and C. liberica. Flowering phenology observations continued daily from July to October 2020, extending to two locations of parapatric populations of three coffee species. Flower morphometric measurements ensued at the peak period of flowering. The results showed some co-anthesis periods among the three coffee species, with C. liberica starting to flower early. Moreover, C. liberica var liberica had the broadest flower diameter and the highest petal number, whereas the tetraploid C. arabica had the lowest. Consequences of flowering phenology and flower structure on a pre-zygotic barrier of spontaneous, as well as, controlled interspecific hybridization among the three coffee species were the discussion focus.

Keywords: Coffea, interspecific crossing, flowering phenology, flower structure, pre-zygotic barrier

Key findings: Co-anthesis events occurred during the peak flowering periods in sympatric or parapatric populations of three coffee species (C. arabica, C. canephora, and C. liberica). Therefore, interspecific hybridization using freshly collected pollen is feasible. These findings could enrich information on a pre-zygotic barrier among C. arabica, C. canephora, and C. liberica species, especially in Indonesia. Breeders, in turn, could utilize the results to manage their future work on interspecific hybridization among these three coffee species.