Télécharger mémoire online étude phytochimique de launaea arborescans et halophila stipulacea, tutoriel & rapport PDF.
Chapter 1: Literature data
ASTERACEAE FAMILY
General introduction
The family of Asteraceae or, alternatively, Compositae, known as the aster, daisy or sunflower family, is one of the largest angiosperm families of a taxon of dicotyledenous flowering plants. It comprises about 1400 genera and more than 25000 species of herbaceous plants, shrubs, and trees, spread throughout the world, and classified over three subfamilies and 17 tribes (Bremer, 1994). The composite nature of the inflorescences of these plants led early taxonomists to call this family Compositae. Though diverse habits and habitats, composites tend to grow in sunlit places, in temperate and subtropical regions. Some Asteraceae plants can share these following characters: ü Various members of the aster family are familiar species in natural habitats, while others are cultivated plants in gardens and some are grown as food (Lactuca sativa) (Lettuce), and Cichorium ( Chicory).
ü Many members of Asteraceae are pollinated by insects, which explain their value in attracting beneficial insects. Many members of Asteraceae are copious nectar producers and are useful for evaluating pollinator populations during their bloom. Centuarea cyanus, Helianthus annuus and some species of solidago are major honey plants.
ü Some species in the aster family have anatomical mechanisms of attaching their seeds to the fur of mammals, for the purposes of dispersal.
ü Phytochemically, species of Asteraceae biosynthesize many several metabolites such polyfructanes (especially inulin) as storage carbohydrates as opposed to polysaccharides, in the perennial taxa. In some taxa, some segments of the family accumulate polyacetylenes, flavonoids, various alkaloids and terpenoids essential oils. But iridoids have never been found (Harborne et al., 1994).
ü Plants in Asteraceae are medically important; sesquiterpenes compounds obtained from them are responsible for allergic contact dermatitis. More than 4000 structures with around 30 different skeletal types have so far been reported from several tribes of this family (Seaman, 1982). Due to their chemo-diversity, the sesquiterpene lactones are the most suitable class of naturals products for chemo-systematic studies within the family (Seaman, 1982, Zdero et al., 1990). It is interesting to note that parthenolides derivatives are important sesquiterpene lactones responsible for the pharmacological activity of many botanical drugs e.g. Fever few (Chrysanthemum parthenium) and Arnica (Arnica montana).
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