Pollen Morphology of Melodorum fruticosum Lour.

The morphology and ultrastructure of pollen grains of Melodorum fruticosum Lour. are described based on observations using a scanning electron microscope (SEM) and transmission electron microscope (TEM). Pollen grains of M. fruticosum were globose or oblate shape,with no visible aperture or any indication of a pole,and the ornamentation was rugulate. The pollen wall was composed of an outer exine and an inner intine layer. The exine consisted of three distinct layers：tectum,infratectum and foot layer. The tectum was continuous and uniformly thickened. The infratectum was mixed with granules and columellae,and nearly one half of the total exine in thickness. The foot layer was composed of undulating foliations. The endexine was homogeneous and lamellated. The intine was two-layered,and varied from two to one half times the exine in thickness. Except for the especially thickened infratectum and foot layer foliations without white line in M. fruticosum,the pollen characters were similar to those of Uvarieae. Moreover,data on the relationship of aperture types,variations of sporoderm thickness and evolution of tectum in Annonaceae were determined and discussed.