Asteraceae Family

Asteraceae Family

• 2.
  COLLEGE : COLLEGEOF AGRICULTURE , JAU , AMRELI B.SC.AGRI. 1ST SEM. COURSE : P.B.G.1.1 TITLE : ECONOMIC BOTANY ROLL NO. : 07 TOPIC : A PRESENTATION OF ASTERACEAE FAMILY (COMPOSITAE) SUBMITTED TO : PROF. R.S.PARMAR SUBMITTED BY : DHAVAL BHANDERI
• 3.
  CLASSIFICATION : DIVISION :ANGIOSPERMS CLASS : DICOTS SUB CLASS : GAMOPETALAE SERIES : INFERAE ORDER : ASTERALES FAMILY : ASTERACEAE
• 4.
  HABIT : These areherbs and shrubs , rarely twiners , e.g. Mikarnia scandens , or trees , e.g. Vernonia arborea . They sometimes have internal phloem . Some genera have latex , e.g. Sonchus , Crepis , Lactuca , Picris , etc.
• 5.
  LEAVES : The leavesare simple , alternate or opposite , rarely compound . INFLORESCENCE : The inflorescence is a head ( or capitulum ) , with an involucre of bracts .
• 6.
  FLOWERS (FLORETS) : Theflowers are of two kinds – the central ones (called disc florets ) are tubular and the marginal ones ( called ray florets ) are ligulate . Sometimes all florets are of one kind , either tubular or ligulate . The disc flowers are regular , tubular , bisexual and epigynous , each usually in the axil of a bracteole .
• 7.
  CALYX : The calyxis often modified into a cluster of hairs called pappus , as in Tridax and Ageratum , or into scales , as in sunflower and Eclipta , or absent , as in water cress (Enhydra) . COROLLA : There are (5) petals. It is gamopetalous and tubular.
• 8.
  ANDROECIUM : The 5stamens are epipetalous. The filaments are free but the anthers united (syngenesious). GYNOECIUM : The carpels are (2) , syncarpous. The ovary inferior , 1-celled with one basal , anatropous ovule. There is one style and the stigma is bifid.
• 9.
  FRUIT : The fruitis a cypsela. The ray florets are zygomorphic , ligulate , unisexual (female) , or sometimes neuter , as in sunflower and epigynous , each usually modified into pappus. Sometimes it is scaly or absent. The Corolla has (5) petals , is gamopetalous and ligulate (strap- shaped).
• 10.
  SYSTEMATIC POSITION OF COMPOSITAE: For its many special characters Compositae is assigned an advanced position , the highest according to Engler , in systematic botany. This means that the family is of recent origin ; fossils of this family have been traced down to only the Oligocene period ( and not further back). Fossil records indicate that the genus Senecio came into existence first and other genera developed from it in due course.
• 11.
   It islikely that Compositae and Rubiaceae arose from a common ancestry. The former also maintains a phylogenetic connecion with Umbelliferae by virtue of inflorescence and floral mechanism.  Compositae is remarkable in many respects : it has the maximum number of species among dicotyledons and some genera with a very large number of species ; its worldwide distribution ; its variety of forms and its very effective mechanism for cross-pollination.
• 12.
  SPECIAL FEATURES : Thespecial features characterizing Compositae as an advanced family are as follows : 1. Predominantly herbaceous forms ; 2. Flowers massed together in a head (a perfect type of inflorescence) with the following decided advantages – i. Greater conspicuousness to attract insects for cross-pollination ; ii. Considerable saving of corolla-material and iii. Achievement of cross-pollination by a single insect within a very short time; 3. Very simple but effective type of floral mechanism to achieve cross-pollination without at the same time losing a chance for self-pollination if the former method fails;
• 13.
  4. Easy accessof insects to the nectary which lies at the base of the style and is protected from rain; 5. Flowers typically pentamerous , gamopetalous , bisexual , epigynous with definite number of stamens and carpels – an almost similar type of floral construction throughout the whole family ; 6. Efficient protection of floral buds by the involucral bracts; 7. Very effective mechanism for seed-(fruit-) dispersal by parachute-like pappus (calyx) or by hooks or glands developing on the fruit.