ASTERACEAE

Chromolaena odorata [Eupatorium odoratum].

Tridax


ASTERACEAE( COMPOSITAE)
One of the largest families.The number of species all over the world around 13000...form more than 10% of the total number of species of flowering plants.
Vegetative characters:Annual or perennial.Mostly herbs,a small proportion shrubby, few are trees or woody climbers.Few species produce stem tubers or rhizomes, many species have a milky sap.Roots and stems commonly contain oil passages.
Leaves : alternate,rarely opposite or whorled,simple or pinnately or palmately lobed divided or compound and exstipulate.
Flowers and Inflorescence:The primary Inflorescence is Racemose head or capitulum.Primary heads often arranged into large inflorescence such as raceme corymb or compound heads.Each head is subtended by an involucre of green or membranous bracts. The number of flowers (florets) in a head varies from few to many but sometimes as in Echinops the heads are reduced to a single flower.The shape of the receptacle may vary from flat,concave,convex conelike.
The flowers are mostly bisexual,sometimes unisexual or neutral. In some all florets are alike while in some the central florets are actinomorphic while parietal are zygomorphic.
Flowers are pentamerous and epigynous.
The Calyx is sometimes altogether absent or represented by scarious five lobed rim at the top of the ovary.Usually it is represented by the pappus or hairs or bristles.
The corolla is of five fused petals.It may be tubular or ligulate
The stamens are five.The filaments are free but anthers are connate into a tube around the style.The stamens are usually included in the corolla tube.
The gynoecium is bicarpellary and syncarpous. The ovary is inferior and unilocular.The style is mostly bifid.
Fruits and seeds: The fruit is an achene often compressed and crowned by pappus of hairs plumes barbs or scales sometimes.The seeds are nonendospermic and with straight embryo.
Small flowers are attractive due to formation of heads and due to ray florets.Nectar is secreted by disc and collects in corolla tube. All of these favours insect pollination. Seeds are adapted for wind dispersal. Some fruits have hooks for animal distribution.
Examples:
The family provides some food,dye and oil yielding and medicinal plants,besides a large number of ornamental garden plants.
Lactuca sativa : cultivated as a salad crop.
Helianthus annus(Sunflower)सूर्यफुल
Carthamus tinctorius(Safflower) Important oil seed crop
Helianthus tuberosus: and Cyanara scoliamus :The roots are used as food
Tagetes minuta (Stinking Roger) and T.patula (French Marigold)Yield a strong aromatic essential oil.used as an antiseptic.
Tanacteum vulgare :(Tansy) essential oil used in rheumatism gout and in chronic ulcers
Taraxacum officinale:(Common Dandalion) drug Taraxacum from tuber useful as laxative and hepatic stimulant.
Spilanthus paniculata: flower heads are chewed to relieve toothache.
Calendula officinalis: The dried ligulate florets form the drug calendula used in sprains and bruises.
Chrysanthemum : A few species yield insecticide Pyrethrum.
The pollen of Ambrosia artemisifolia and Parthenium hysterophorus cause hay fever and skin allergies respectively.
Ornamentals:
Helianthus
Tagetus(Marigold) T.erecta(African marigold) T. patula (French Marigold)
Dahlia Chrysanthemum Cosmos Zinnia Coreopsis Aster Gaillardia Dimorphotheca
Calendula(Pot Marigold)
Centaurea (Sweet sultan)