Abstract
The marine seagrasses form an ecological and therefore paraphyletic group of marine hydrophilus angiosperms which evolved three to four times from land plants towards an aquatic and marine existence. Their taxonomy is not yet solved on the species level and below due to their reduced morphology. So far also molecular data did not completely solve the phylogenetic relationships. Thus, this group challenges a new definition for what a species is. Also their physiology is not well understood due to difficult experimental in situ and in vitro conditions. There remain several open questions concerning how seagrasses adapted secondarily to the marine environment. Here probably exciting adaptation solutions will be detected. Physiological adaptations seem to be more important than morphological ones. Seagrasses contain several compounds in their secondary metabolism in which they differ from terrestrial plants and also not known from other taxonomic groups. Some of these compounds might be of interest for commercial purposes. Therefore their metabolite contents constitute another treasure of the ocean. This paper gives an introduction into some of the most interesting aspects from phylogenetical, physiological, and metabolic points of view.
Highlights
Seagrasses are a paraphyletic group of marine hydrophilus angiosperms which evolved three to four times from land plants back to the sea
There is no data set of molecular markers available which resolves all taxonomically accepted seagrass species, and more work has to be done to close this gap of knowledge
In contrast to terrestrial plants, where aquaporins are involved in water transport, these in situ results suggest a role in the water balance and/or solute transport in the different organs and tissues of Posidonia oceanica
Summary
Seagrasses are a paraphyletic group of marine hydrophilus angiosperms which evolved three to four times from land plants back to the sea. The following characteristics can be used to define a seagrass species It lives in an estuarine or in the marine environment, and nowhere else. The roots can live in an anoxic environment and depend on oxygen transport from the leaves and rhizomes but are important in the nutrient transfer processes [1]. This paper aims to highlight some fascinating and sometimes hidden aspects of seagrass physiology and their metabolites and focuses on the distinctiveness of seagrasses from an evolutionary point of view. Maybe it encourages protecting the invaluable ecosystem of seagrass meadows
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