Pollen morphology of Annonaceae from the Bicol Region, Philippines

Annonaceae is one of the most prominent families with diverse pollen morphology. The present study aimed to investigate and describe the pollen morphology of 12 species of Annonaceae from the Bicol Region, Philippines. The pollen grains were subjected to acetolysis and described using a scanning electron microscope, and the hierarchical cluster analysis was done to cluster the pollen grains with similar characters. The 12 Annonaceae species share characters such as monads, inaperturate, and isopolarity, but they formed three distinct clusters based on pollen size. Their polar axis (PA) and equatorial diameter (ED) are statistically significant due to their variability, with PA ranging 36.41±15.86 µm and ED 28.27±14.27 µm. The polar length-to-equatorial diameter (PA/ED) ratio is 1.32, with mostly sub-prolate shape. Exine ornamentations showed significant variability among the 12 Annonaceae species with echinate, rugulate, scabrate, psilate, and verrucate. The pollen morphology of the two endemic species, namely Friesodielsia lanceolata (Merr.) Steenis and Goniothalamus elmeri Merr. is first reported here. Collections of more endemic Philippine Annonaceae species are deemed necessary to comprehensively analyze their pollen characters, which are helpful for infrageneric relationships within the family.