Abstract: Abstract The pollen morphology and ultrastructure of pollen wall of Pinus yunnanensis Franch. were examined with light microscope, scanning electron mi-croscope and transmission electron microscope. The pollen grains have sacci on both sides of body. The sacci are reticulate under LM and SEM. The exine surface contains tuberculate ornamentation under SEM. TEM examination reveals that the pollen wall from top to bottom includes sexine, nexine, incomplete outer intine, inner intine. Sexine is composed of tectum, baculum and foot layer. Nexine is homogeneous in structure and dark in colour. Exine and sacci are made of sporo-pollenin. The incomplete outer intine is composed of callose. The PAS action of the inner intine is positive. It is interesting to note that intine of the pollens kept for one year has changed in structure. Adhesion of the pollen mother cells, tetrad and pollen grains were described and analysed. The pollen morphology and size were various. Heteromorphic pollen grains without saccus, with one saccus, two abnormal sacci, three sacci and four sacci w.ere observed. These sacci are also reticulate under LM and SEM. The rate of the heteromorphic pollen grains is about five percent. The corpora of some heteromorphic pollen grains are larger than that of normal pollen grains. They are maybe polyploid. According to the observations, one of the reasons causing the heteromorphic pollen grains is probably the abnormal development and fusion of PMCs and tetrads.

Key words: Pinus yunnanensis