POLLEN MORPHOLOGY AND TAXONOMY OF EURASIATIC SPECIES OF THE GENUS BUXUS (BUXACEAE)

Pollen morphology of 33 Eurasiatic taxa of the genus Buxus was investigated by light and scanning electron microscope. The pollen is generally pantoporate. In comparison with the American and African sections of the genus, in which evolutionary lines from 3-colporate to pantoporate conditions are found, the Eurasiatic species are more derived. A tendency to diminish pore size (empty set from 6.0 to 0.5-1.0 mum) as well as to increase number of apertures (from 12 up to 34) is correlated with geography, ranging from tropical SE Asia to the north and west parts of the area. Based on SEM details of exine 6 pollen types are described. Quantitative characters are listed, and LM and SEM illustrations are given. Pollen characters and evolutionary trends are discussed. Supposed evolutionary trends in pollen morphology of Eurasiatic Buxus are (primitive --> derived character state): Pori round --> irregularly shaped, distinct --> indistinct margin, large --> small, few --> many. Exine reticulate --> reticulate-verrucoid --> verrucoid-pilate. Reticulum continuous --> interrupted. Surface of muri smooth --> spinulate. The results confirm a close relation between the Eurasiatic sections Buxus and Eugeniobuxus Hatusima. The subsections Sessiliflorae Mathou and Pedicellatae Mathou of section Buxus are to be rejected. SE Asia is considered to be centre of diversity of the Eurasiatic Buxus species. Beside Central America and southern Africa it is one of the evolutionary centres of the genus Buxus.