POLLEN MORPHOLOGY OF DILLENIACEAE IN THAILAND

Pollen morphological studies on 18 species of Dilleniaceae from Thailand were conducted using dehydrated samples under a light microscope as well as scanning electron microscope. The pollen grains are monad, radially symmetrical, and isopolar. The pollen grains are small to medium in size with an equatorial diameter of 15.61-34.51 mu m and polar diameter of 13.66-31.39 mu m in the equatorial view. Most of the species of the genera Dillenia and Acrotrema are tricolpate, while D. philippinensis and D. ovata are tricolpate or occasionally tetracolpate, whereas the genus Tetracera is tricolporate. Variation is found in the shapes (oblate spheroidal, suboblate, subprolate, and prolate spheroidal), exine sculpturing (punctate, reticulate, regulate, and reticulate-verrucose), distance between the apices of two ectocolpi, colpus length, colpus width, porus length, porus width, and exine thickness. For numerical analysis, 13 qualitative characteristics and five quantitative characteristics were used for the principal component analysis and cluster analysis to determine the potential of the pollen morphological characteristics to be used to determine the species relationships. The results of the two numerical analysis methods showed that pollen morphological data could be used to classify the genera Acrotrema, Dillenia, and Tetracera into groups.