Pollen morphological investigation of selected species of family Asteraceae from Pakistan by using light and scanning electron microscopy

A light and scanning electron microscopy technique was conducted to investigate the palynological features of 19 species belonging to 15 genera of the family Asteraceae. The species under investigation yielded pollen in a range of shapes, including spheroidal, prolate, and subprolate. Trizoncolporate, Tricolporate, and Tetracolporate are the three types of pollen apertures observed in examined species. Except for Gazania rigens, which has reticulate ornamentation under SEM, the exine pattern in all studied species is echinate. The majority of the species had isopolar polarity, whereas some members were apolar and heteropolar. The quantitative parameters that are polar to equatorial diameter, P/E ratio, length of colpi, width of colpi, length of the spine, width of spine, and exine thickness was measured by using light microscopy. The Coreopsis tinctoria had the lowest mean polar 19.75 mu m to mean equatorial diameter 18.25 mu m while the Silybum marianum had the highest polar 44.7 mu m to equatorial 48.2 mu m value. The value for colpi length/width was highest in Cirsium arvensis and lowest in C. tinctoria, measuring 9.7/13.2 mu m and 2.7/4.7 mu m, respectively. The spine length varied from 0.5 mu m in Sonchus arvensis to 5.5 mu m in Calendula officinalis. Verbesina encelioides had the highest exine thickness measurement (3.3 mu m), whereas S. arvensis had the lowest (0.3 mu m). The pollen surface of Tagetes erectus, has the highest number (65) whereas the lowest spines number (20) is found in S. arvensis. A taxonomic key based on pollen traits is provided for quick identification of the species. Significant implications for the systematics of the Asteraceae family can be drawn from the reported pollen's quantitative and qualitative data.