Asteraceae : Morphological Diversity of Families to know about this topic read this full article.
Asteraceae is the largest family of flowering plants containing at least 1528 genera and 22750 species distributed mainly in temperate and subtropical regions.
Selected Indian genera: Ageratum, Chrysanthemum, Dahlia, Eclipta, Heliathus, Sonchus, Tagetes.
Herbs, shrubs or trees (Veronia arborea).
Vegetative Charaters of Asteraceae:
Stem: Herbaceous, Aerial, erect, branched and with milky sap.
Leaves: Simple or compound, spiral or opposite (rarely whorled),
Floral Characters of Asteraceae
Inflorescence: Capitulum (Head) with distinct involucre cup formed of bracts. The capitulum may be solitary or may be arranged into cymes. The marginal sterile or female flowers are called ray florets, these are ligulate.
The central bisexual flowers are called Disc florets.
Disc Florets: Actinomorphic, hermaphrodite, tubular epigynous and bisexual.
Calyx: Calyx in Asteraceae family is represented by a ring of small teeth of numerous hairs or scales, so called pappus (Ageratum conyzoides).
Corolla: 5 petals, gamopetalous and tubular.
Androecium: 5 stamens. Epipetalous, syngenesious.
Gynoecium: Bicarpellary, syncarpous, ovary inferior, unilocular with single anatropous ovule, style is simple, stigma bifid.
In ray florets Zygomorphic, Pistillate (female) ,
ligulate and epigynous.
Corolla: 5 petals, gamopetalous, strap shaped (ligulate),
Fruit: Cypsela often crowned by persistent pappus.
Seed: Non-endospermic, embryo straight.
Gynoecium- Bicarpellary and syncarpous, ovary inferior and unilocular with basal placentation. Style mostly bifid.
Habit: Annual herb
Root: Tap root, branched
Stem: Aerial, erect, cylindrical, branched, solid, hairy and soft.
Leaf: Ramal and Cauline, simple, petiolate, exstipulate, opposite, ovate, serrate margins, acute and hairy, venation reticulate unicostate.
Inflorescence: The primary aggregation of flowers is a head ( Capitulum) clusterd in a Corymbose inflorescence. The corymb are terminal heads with no distinction into rays and disc florets.
Flower: sessile, Bracteate, ebracteolate, complete, pentamerous, actinomorphic, bisexual and epigynous, flower violet in colour.
Calyx: Sepals 5, but reduced to scaly structure called pappus, aestivation valvate.
Corolla: Petals 5, gamopetalous, tubular, violet in colour, aestivation valvate.
Androecium: Stamens 5 alternate with the petals and epipetalous, filaments short, anthers long syngenecious, basifixed. Bithecous, introse, dehiscing longitudnally.
Gynoecium: Ovary inferior, bicarpellary, syncarpous, unilocular with only one ovule on basal placenta. Style long divided into two arms. Stigmas long, flattened at the tip, glandular papillae present on the stigma.
Fruit: A Cypsela, black in colour. At the tip of the fruit are present 5 scales of the calyx.
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