泽泻科的花粉形态研究

POLLEN MORPHOLOGY OF THE ALISMATACEAE

本文对泽泻科11属27种代表植物的花粉进行了光学显微镜、扫描电镜和透射电镜观察。在系统描述了该科及各属植物花粉形态的基础上,将泽泻科植物的花粉划分为3种类型,即少果泽苔草型、慈菇型和泽泻型。根据花粉形态特征的比较,并依据泽泻科植物祖先类群的花粉具有船形、具单沟萌发孔、花粉外壁具明显的刺状纹饰、覆盖层完整无通道等特征,作者认为泽泻科植物花粉形态的如下演化趋势是明显的:由船形演化为卵球形、球形和多面体球形;由单沟萌发孔经过一无孔的中间类型演化为散孔类型;孔膜由光滑演化为具颗粒和小刺;萌发孔不内陷进化到内陷;花粉粒外壁的刺状纹饰逐渐过渡为颗粒状纹饰或者消失,以及覆盖层由无通道到具细通道和通道。

Pollen morphology of 27 species representing 11 genera of the Alismataceae was studied by light microscope (LM), scanning electron microscope (SEM) and transmission electron microscope (TEM). Based on the observed pollen characters, three types of pollen were distinguished; (A) The Caldesia-oligococca type. Disc- or lens-shaped, with 2 pores (pores probably equatorially orientated, opposite each other) ; pores situated in depressions, more or less circular with fimbriate, fold-like structures arising from the margins; the exine granulate or slightly spinulate under SEM. (B) The Sagittaria type. Spheroidal, pantopo-rate; pores in hardly sunken depression, delimited or not sharply delimited in outline, covered with coarsly or sparesly granulate or spinulate membranes; the exine spinulate with spinules 1~2 jum long. (C) The Alisma type. Rounded to polyhedral pantoporate; pores covered with granular membranes and circumpolar ornamented area, situated in depressions; the exine smooth to finely spinulate with spinules less than 0.5 m long. The exine structure of all examined materials under TEM is three-layered; tectum, columellae and footlayer. The endexine is neither distinguished nor separated from the footlayer. The most primitive alismataceous pollen grains might be boat-shaped, monosulcate, with hardly sunkenpores, smooth pore membranes and exine spinulate exine without tectum perforation. The pollen of the Alismataceae is most likely derived from the monosulcate ancestor (possibly via nonaper-turate intermediate) by an increase in pore number and a reduction in supratectal ornamentation. The evolutionary trends of alismataceous pollen are described as follows; (A) Pollen shape; from boat-shaped type to polyhedral one via a spherical intermediate condition, then to bilateral pollen, the highly derived. (B) Aperture; from the primitive monosulcate type to the pantoporate one via a nonaperturate condiation. (C) Aperture membrane; from smooth to granulate and spinulate. (D) Aperture not sunken was primitive; while sunken condition de- rived. (E) The sculpture of exine; from spinulate to granulate or spinuleless. (F) Tectum with microchannels or channels might be derived, that without channels the most primitive.