Cordia subcordata (Boraginaceae), a distylous species on oceanic coral islands, is self-compatible and pollinated by a passerine bird

• Published in: Plant ecology and evolution Vol. 153; no. 3; pp. 361 - 372
• Main Authors: Wang, Xiangping, Wen, Meihong, Wu, Mingsong, Zhang, Dianxiang
• Format: Journal Article
• Language: English
• Published: Botanic Garden Meise and Royal Botanical Society of Belgium 23.11.2020; Royal Botanical Society of Belgium; Meise Botanic Garden
• Subjects: Cordia Subcordata; Distyly; heterostylous self-inc; Heterostylous Self-Incompatibility; Oceanic Island; Passerine Pollination; REGULAR PAPERS
• ISSN: 2032-3913; 2032-3921
• DOI: 10.5091/plecevo.2020.1757

Background and aims-Distyly is usually rare on oceanic islands, which is probably due to the difficulty for distylous plants to colonize those islands. However, Cordia subcordata was observed to be distylous with short- and long-styled morphs on the Xisha Islands in the South China Sea. To characterize the reproduction system of Cordia subcordata and to understand how this distylous species maintains itself on these islands, we studied its reproductive and pollination biology. Methods-Seed set and pollen tube growth under manipulated intermorph, intramorph, and self-pollination were examined to investigate self-incompatibility in the species. The number of pollen grains deposited on the stigmas after a single pollinator visit were counted to investigate the pollination efficiency of different visitors. Key results-Our study indicated that Cordia subcordata shows reciprocal herkogamy as is typical in distylous species. Pollen tubes could reach the base of the style and move into the ovules under all the manipulated pollination treatments in both morphs. Seed set resulting from four hand-pollination experiments did not show any differences between both morphs, suggesting that Cordia subcordata lacks heterostylous self-incompatibility. The most frequent flower visitors, Zosterops japonicus and Apis cerana, were observed foraging on the large volumes of nectar and pollen grains, respectively, with Zosterops japonicus being the most effective pollinator, depositing large number of pollen grains on the stigmas during their visits. Conclusions-Our findings show that Cordia subcordata established itself and persists in the archipelago by producing fruits through a combination of self-compatibility and pollination by the most common passerine bird on the oceanic islands.