The terrestrial and marine angiosperm flora seem inexhaustible since only a small part of the 400'000 vegetable species known were investigated from phytochemical and pharmacological aspects, and that each species can contain up to several thousands of different components Actually, the development of the spectroscopic methods coupled with a good extraction and purification techniques, has contributed to the phenomenal success of natural product chemistry, and has given another ways for discovering new structures.In this light, the endemic Algerian plant Launaea arborescens and the marine phanerogam Halophila stipulacea, has resulted in the isolation of a plethora of natural products, including new terpenoids and new flavonoids, and which allowed us to get useful information for either chemo-taxonomic or ecological studies of sea grasses and terrestrial plants. The elucidation of the obtained structures was achieved by means of spectral methods mainly NMR techniques.