PALYNOLOGICAL INVESTIGATION OF THE TRIBE HELIANTHEAE (ASTERACEAE) IN PAKISTAN AND ITS TAXONOMIC IMPLICATIONS

Pollen morphology of eight genera and 11 species belonging to the tribe Heliantheae -Asteraceae viz., Blainvillea Cass., Eclipta L., Helianthus L., Parthenium L., Sphagneticola O. Hoffm., Verbesina Cav., Xanthium L. and Zinnia L. have been examined under the Light Microscope (LM) and Scanning Electron Microscope (SEM). Pollen grains are generally radially symmetrical, isopolar, mostly prolate-spheroidal to prolate rarely oblate-spheroidal or spheroidal. Tectum is usually echinate except in Xanthium and Parthenium which have micro echinate (spinulose) tectum. However, significant variation in qualitative and quantitative pollen morphological characters has been observed in pollen shape, polar length and diameter of equatorial axis (13-25 µm), exine thickness 1.31-3 µm and exine ornamentation micro echinate-echinate, spine length 1 to 4 µm, and tectum in between spines such as, punctate, to sub-psilate, rarely rugulate or granulate. Based on the exine ornamentation and cluster analysis two distinct pollen types are recognized viz., Pollen type-I Helianthus type (based on echinate), and pollen type-II Xanthium type (Micro echinate). The results of this study have shown that palynological characters are significantly helpful at specific levels.