Exploring intraspecific pollen morphology variation in Apocynaceae: A roadmap for horticultural innovation

This study aimed to examine the pollen and pollinia morpho-structure of 18 horticultural Apocynaceous species. Advanced light and scanning electron microscopy (LM and SEM) were used to elaborate on and examine the systematic importance of pollen and pollinia micromorphology. Pollen grains were first acetolysed, which was followed by visualisation of their sculpturing features. The quantified data were subjected to statistical tools to elucidate dendrogram clustering and principal component analysis to reveal pollen/pollinia morphotypes. The size of pollen is variable, ranging from 113.45 μm in Cascabela thevetia to 23.4 μm in Alstonia scholaris. The study revealed tetrad, tetraporate, and tricolporate grains. Sculpturing (exine ornamentation) varies from reticulate perforate to reticulate. Pollinum shape was observed to be narrow oblong, obovate, orbicular, and reniform. Reticulate-psilate sculptural features were prominent among pollinia surfaces. Based on examination, it was ascertained that the minimum exine thickness in Periploca aphylla was 4.9 μm, whereas the corresponding number in Cryptolepis dubia was 1.35 μm. Taxonomic identification keys were constructed separately based on pollen/pollinia characters to identify the Apocynaceous taxa. In the presented study, seven pollen shapes were observed: from oblate to per prolate. The findings confirm that morphopollinic traits differ amongst genera of Apocynaceous species. However, these features can be used to distinguish the Apocynaceous taxa. The results show that structural characteristics of pollen and pollinia can help accurately identify Apocynaceous species.