Morphology And Anatomy Structure Of Phyllospadix Iwatensis Makino And Their Adaptation To The Marine Environment

As one of the marine submerged higher plants, Phyllospadix iwatensis Makino has the important value of ecology and fisheries and it is also an important kind of natural resources of Chinese marine medicinal materials. Although this species is now in the endangered state, its fundmental research is still scarce. In this study, P. iwatensis was comprehensively investigated to study its morphological and anatomical features and explore their adaptation to marine environment. The results showed that the plant body of P. iwatensis has evolved in many ways on its morphological and anatomical features, which are mainly represented as follows:The root end inflated covering with dense root hairs which is conducive to enhance the ability to attach and absorb nutriment; its epidermal cell wall six-side thickened like the primary cell wall, along with multilayers collenchyma of the outside cortex formed a mechanical tissue area; Leaf sheath contained rich mechanical tissues in its inner side strengthening the resistance to the strong current. The male inflorescence without pistillode, while the female inflorescence existed both pistils and staminodes, with a number of paddle-like retinacules on both side of inflorescence axis. The pollens were filamentous to contribute to the pollination. They were transported by a mixed mode of hydrophilous pollination and submarine pollination. The nutlet densely beared retrorsely long bristles that can be very useful to anchor the fruit to the rocky sediment in strong current.This paper has also estimated the divergence time of Phyllospadix based on ITS and matK region, using a Bayesian relaxed-clock approach and a fossil time for calibration. The chronogram showed that the evolution process of Phyllospadix can be trace back to the Eocene of Paleogene, which was between 38.9 and 33.4 million years ago. In consider with the paleogeology and paleoclimatology condition in Eocene, we believe that the division of Phyllospadix was related to the sea-level drops. During the ancestors of Zosteraceae species migrated along the ocean dropping direction, some of the individuals, who finally diverged into the modern Phyllospadix, had completed major structure and function evolution to adapt the rocky and gravel substrate. This divergence event has reflected the important process of adaptation evolution for species, and it will undoubtedly contribute to expand our knowledge on the origin of life. These results not only provide new insights into the adaptative features of marine submerged high plants, but also deliver the information of morphology structure for the study of marine medicinal plant resources while shedding some light on the application of ecological remediation P. iwatensis.