八种苏铁植物叶轴的比较解剖研究

对苏铁科和泽米铁科8种苏铁植物,即台湾苏铁(Cycas taiwaniana)、海南苏铁(C·hainanensis)、元江苏铁(C·parvulus)、单羽苏铁(C·simplicipinna)、滇南苏铁(C·diannanensis)、越南篦齿苏铁(C·elon-gata)、长刺大泽米铁(Macrozamia longispina)、双子铁(Dioon edule)的叶轴横切面结构进行了比较研究,以期为苏铁植物的系统演化和分类进一步提供解剖学依据,并探讨其解剖结构与生态的适应机制。结果表明,较原始的苏铁科和较进化的泽米铁科叶轴的横切面结构无论在表皮、机械组织、基本组织和维管组织,还是在后含物方面都存在着明显的不同;泽米铁科的大泽米铁属与双子铁属差异也较大;苏铁科科内的6个种则相似性稍大,表明它们是亲缘关系较密切的类群,但每个种都有各自的结构特点。越南篦齿苏铁的维管束排列方式和数目的增加方式与泽米铁科两个种的相似,因此推断它处于较进化的地位。研究还发现苏铁科种类的叶轴的近轴面均像叶片那样具有栅栏组织状同化组织存在。苏铁类植物叶轴具有旱生植物的解剖结构特征:角质层较厚、表皮细胞壁厚、机械组织发达、晶体较多、分泌道和维管束数目较多等结构特征。这些对研究苏铁纲各科及种类之间的进化与亲缘关系提供了佐证,同时揭示了苏铁纲这类古老的植物类群其多个属的种类能够经历如此漫长的地质年代而幸存下来,是由于其在长期演化过程中均形成了这些独特的结构特征,因而具备了相对应的生理功能,能够在恶劣的自然环境下,具备耐干旱、贫瘠、高温及耐盐碱等逆境的结果。

Comparative Anatomic Studies on Rachis of Eight Species of Cycads

This article conducted comparative anatomy of rachis of six species of Cycadaceae and two species of Zamiaceae, i.e., Cycas taiwaniana, C.hainanensis, C.parvulus, C.simplicipinna, C.diannanensis, C.elongata, Macrozamia.longispina and Dioon edule in transverse section, in order to provide anatomical evidence for a better understanding of the systematic position, taxonomy and to discuss its anatomy structure and the ecological adaption mechanism. The results showed that there were significant differences between Cycadaceae and Zamiaceae in epidermis, mechanical tissue, ground tissue, vascular tissue and ergastic substance and so on. The rachis structure of genus Dioon was also different from genus Zamia. The 6 species of Cycadaceae are more similar to each other, particularly among C.taiwaniana, C.hainanensis, C.parvulus, C.diannanensis, C.simplicipinna, which manifests they are closely related to one another, but each species has its own structure characteristic. The arrangement and the process of the increase of vascular bundle number of C.elongata is similar to the two species of Zamiaceae which implied that its status is comparatively derived in Cycas. The study discovered that there are assimilating tissue which like the shape of palisade tissue in adaxial surface of rachis in all species of Cycas. The rachis of these cycads had structure characteristic of xerophytes, i.e., thicker cuticular membrane, developed mechanical tissue, the more secretion, crystal and secretory canal and more number of vascular bundles etc. These results provided evidence to study the evolution and relationship between different families and species of the Cycadopsida, and revealed the fact that primitive and ancient cycads can exist in the geological history is because cycads unique structure characteristics have been evolved so that they can adapt to various evironment such as drought, extreme heat, barren, and salt alkaloid and other harsh environment.