美乐多（Melodorum fruticosum Lour．）花粉形态观察

利用扫描电子显微镜（SEM）和透射电子显微镜（TEM）观察了美乐多（Melodorum fruticosum）的花粉形态特征。美乐多花粉为球形或扁圆形的单粒花粉，外壁纹饰为微褶皱状，有点状凹陷，无任何萌发孔或萌发沟。花粉外壁由外壁外层包括覆盖层（连续）、覆盖下层、基足层（1～3层薄片层结构，偶断裂或扭曲至6～10层）和外壁内层（连续）组成。其中，覆盖下层，其厚度为整个花粉外壁厚度的1／2，为混合型结构，即小柱状和颗粒状同时存在，但以颗粒状为主。花粉内壁分为内壁外层和内壁内层，其厚度逐渐变薄。美乐多的花粉特征（单粒、无萌发孔或沟、覆盖层连续、基足层为薄片层结构、花粉外壁内层薄等）与紫玉盘族其他类群一致。

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.