Floral Biology of Mitreola petiolata and M. sessilifolia (Loganiaceae): Chasmogamous Flowers with Massive Post-Anthesis Precocious Pollen Germination

Mitreola petiolata and M. sessilifolia in the Loganiaceae are similar wetland annuals occurring in tropical, subtropical, and temperate regions in the southeastern U.S., Africa, Asia, and Oceania. The flowers of both species have previously been described to open briefly with an apparent window for outside pollination, followed by flower closure and massive pollen germination within the anthers with pollen tubes covering the adjacent stigma. The phenomenon was documented with field observations, floral dissections, and light and scanning electron microscopy. Both species open their flowers for a brief 6–8 hour window. Subsequently, pollen germinates within the closed or closing flower with pollen tubes completely covering the stigma. The prevalence and importance of selfing by precocious pollen germination are discussed.