|Keywords (Extracted from title, table of contents and abstract of thesis)
asteraceae, pollen morphological characters, asteraceae , polliniferous material, pollen outline, onopordum laptolepis, hieracium vulgatum, cousinia onopordioides, cyathocline lutea, chrysanthemum murifolium, tricholepis furcata, brachyactis pubescens, biden pilosa, arctium lappa, scorzonera laciniata, gaillardia aristata
Pollen morphological characters of family Asteraceae have been investigated from Pakistan. This account includes 14 tribes representing 97 genera and 300 species. Pollen study was conducted in Department of Biological Sciences, Quaid-i-Azam University, Islamabad during 2001-2004. The dried polliniferous material for the present investigation was obtained from the herbarium of Quaid-i-Azam University (ISL), Islamabad. Fresh material of some species was also collected from Islamabad and the adjoining areas of Rawalpindi. The main pollen characters (which have been observed in the present task) are equatorial diameter, polar diameter, P/E ratio, exine thickness, spine length, number of spine rows between colpi, shape in polar view, shape in equatorial view, pollen class, aperture type and sculpturing. Pollen characters such as size, shape, exine thickness, spine length, spine number and aperture type are found to be considerably important. Pollen grains are usually radially symmetrical, isopolar and isodiametric. Pollen outline is prolatespheroidal, spheroidal, angular, circular, semi-angular, lobate, semi-lobate, inter-semilobate, circular semi-lobate to rectangular in polar view and prolate-spheroidal, spheroidal, prolate, oblate-spheroidal, perprolate, suboblate, rhomboidal to sub-rhomboidal In equatorial view. There is a considerable debate for the spinate and spineless pollen In Asteraceae. Among 300 species, 67 species were recorded to be with spineless pollen while 233 species are found to have spinate pollen. This divergence separate the family Asteraceae into two major groups i.e. the species with spinate pollen and the species with spineless pollen. The presence or absence of spines represents a trend of evolution of spine reduction within the family Asteraceae indicating that the spineless pollen is an advance character. This pollen feature would help to establish and improve phylogenetic relationships and classification of Asteraceae.
Pollen grains are trizonocolporate, tetrazonocolporate, pentazonocolporate, hexazonocolporate and octazonocolporate, in different tribes of the family. The range of maximum/minimum pollen sizes in various tribes of Asteraceae is quite variable. Onopordum laptolepis has the highest pol1en diameter (62.8 um) and Hieracium vulgatum can be distinguished due to the lowest (J 8.0 um) pollen diameter. Cousinia onopordioides has been found to be the highest (64.9 um) in equatorial diameter while Cyathocline lutea is the lowest (16.0Jlm) in equatorial diameter. Chrysanthemum murifolium is recorded to be the highest (1.36) in P/E ratio whereas Cousinia onopordioides is reported to be the lowest (0.34) in P/E ratio in Asteraceae. P/E ratio is found to be helpful in grouping of different species of various tribes in the family. There is a great range of variation in exine thickness, which has proved to be useful at specific level. Tricholepis furcata has been observed to be the highest (14.3 um) in exine thickness and Brachyactis pubescens can be distinguished due to the lowest exine thickness (1.4~lm). The pollen spine character is found to be the most diagnostic feature in Asteraceae. Biden pilosa and B. tripartita has the highest spine length (7.2 um) and Arctium lappa can be distinguished due to the lowest spine length (1.5Jlm). Maximum number of spine rows between colpi (12-]6) has been noted in Scorzonera laciniata whereas lowest spine number (3) has been recorded in Gaillardia aristata.
Among the 300 species investigated for pollen morphology 70 species were new reports and four endemic species. In the present investigation Cousinia buphthalmoides, C. haeckeliae, C. heliantheae and c. oxytoma are the only genera which have a very different shape of circular to semi-lobate pollen in polar view and prolate to sub-rhomboidal in equatorial view. Distinct pollen shape distinguished the genus Cousinia and Echinops from rest of the genera in the tribe Cardueae. Quite different pollen morphology of the genus Cousinia and Echinops in the tribe Cardueae suggests the segregation of tribe Cardueae into two groups with respect to the classification of the tribe on the basis of pollen morphology.