Morphological diversity of pollen grains within the flowering stages of Tecoma stans (L.) Juss. ex Kunth

The study of the morphology of pollen grains is essential to understand plant evolution, adaptation, diversity and discrimination of taxa. This study aims to determine the importance of choosing the perfect stage of flower development in the study of pollen morphological characters as a taxonomical tool. In this work a woody, perennial street tree Tecoma stans was chosen as a model species belonging to family Bignoniaceae. Tecoma stans has many polymorphic forms native to North America and flourished in hot climates. This tree is commonly planted in both Cairo and Alexandria streets. Samples of flower buds in nine different stages were gathered from five to six different trees from March to June 2023. Non-acetolysed pollen grains were investigated using both light and Scanning electron microscopes. The results showed that pollen density, size, shape beside colpi length as well as their state varied between the different developmental flowering stages and cannot be relied on taxonomical decisions, while exine ornamentation slightly differed between the pollen grains from stage two to nine, but it was faint in immature flower bud (stage one). This study confirms that we must be precise in choosing the correct flower stage in pollen morphological studies to obtain significant morphological description. The results obtained revealed that the aperture type is more stable than pollen shape and size.