Family Asteraceae

Systematic Position

Division: Angiospermae

Class: Dicotyledonae

Subclass: Gamopetalae

Series: Inferae

Order: Asterales

Family: Asteraceae (=compositae)

Commonly known as sunflower family. It is the largest family in dicots. It includes about 900 genera and 13,000 species. It has a cosmopolitan distribution. There are around 100 species in India.

Characteristic Features

• Habit: Mostly annual herbs, rarely shrubs and trees.

fig. 27.38 Habit, L.S. of inflorescence and florets

• Root: Taproot system, branched.

• Stem: Herbaceous or woody, erect, branched.

• Leaves: Simple, alternate or opposite, exstipulate, petiolate, hairy, reticulate venation.

• Inflorescence: Head or capitulum, terminal or axillary. Florets surrounded by an involucre of bracts.

• Flower: Bisexual, pentamerous, heterochlamydeous, epigynous.

• Ray florets: Towards periphery, sessile, bracteate, pistillate or neutral, zygomorphic, ligulate.

• Calyx: Absent or hairy pappus, or scaly persistent.

• Corolla: Petals 5, polypetalous, ligulate.

• Androecium: Absent.

• Gynoecium: Bicarpellary, syncarpous, unilocular, one ovule, the locule, basal placentation, style narrow, stigma branched, ovary inferior.

• Disc Florets: Towards the centre, bracteate, bisexual, actinomorphic, tubular, epigynous.

• Calyx: Absent or modified into pappus.

• Corolla: Sepals 5, Gamosepalous, tubular.

• Androecium: Stamens 2, epipetalous, syngenesious dithecous.

• Gynoecium: Bicarpellary, Syncarpous, unilocular, one ovule, on basal placentation style single, stigma bifid.

• Neutral florets: Both androecium and gynoecium are absent. Remaining characters similar.

• Fruit: Cypsela.

• Seed: Non-endospermic.

• Floral formula:

Ray florets

Disc florets

Neutral florets

fig. 27.39 Types of florets, their L.S. floral parts, floral diagram and floral formula

Common Examples

Edible

1. Lactuca sativa (Lettuce)

2. Elephantopus - Leaves edible

3. Helianthus tuberosum - tubers edible, seeds yield oil

Medicinal

1. Carathamus tinctorius - Oil used for treating injuries

2. Cynara scolymus - flowers are used for treating diabetes

3. Artinesia obisynthium - yields santonin used for treating worms

4. Xanthium stramonium - leaves used for treating tooth ache

Ornamental

1. Helianthus annus sunflower yields oil

2. Tagetus erectus - marigold

3. Chrysanthemum species

4. Cosmos species

5. Veronica species

6. Zinnia species

fig. 27.40 Examples of Family Asteraceae