Asteraceae: Characters, Economic Importance, Distribution and Types

 Asteraceae (Compositae) 

(Sunflower family)

Diagnostic characters of Asteraceae family:

1. Habit: Annual or perennial herbs or small shrubs or small tree,s or climbers.

2. Roots: Fibrous tap root.

3. Stem: Herbaceous; spiny or without spines; cylindrical, hairy.

4. Leaves: Petiolate (its a kind of leaves that contains leaf-stalk or petiole); alternate or opposite; simple; exstipulate.

5. Inflorescence: Capitulum (is a head) surrounded at the bases by a group of involucres. The receptacle is flat. The flowers in the receptacles are florets. There are two types of florets:

(a) Homogamous: In this case, all flowers are of same kind.

(b) Heterogamous: In this case, two types of flowers are present in the capitula. Example: Sunflower, Sunflower has two different kinds of small flowers, disc florets and ray florets.

i- The disc florets are present in the central region. They are tubular and bisexual.

ii- The ray florets are present towards the periphery of the plant. They are pistillate or neuter.

6. Flower: Sessile (pedicel absent), ebracteate, actinomorphic (radial symmetry/i.e. like star fish or a flower of a daisy), or zygomorphic, pentamerous regular or irregular, complete or incomplete, unisexual or hermaphrodite, epigynous.

7. Calyx: Poorly developed, generally represented by ring of 5 small teeth. They maybe present in the form of small scales or hairs or bristles.

8. Corolla: Gamopetalous (kind of flower in which petals are fused toghter foming a funnel shape), tubular with 5-5 lobed or ligulate with 3-4 teeth. Sometimes bilabiate.

9. Stamens: 5 Stamens rarely 4; epipetalous (its a position in which male reproductive part is connected to the petals of flower); syngenesious (filament free anther united); forming a tube which encloses style.

10. Carpel: Bicarpellary; syncarpous; stigma bifid; ovary inferior; placentation basal.

11. Fruits: Achenial one-seeded cypsela.

12. Seed: Non-endospermic seed.

Floral formula of Asteraceae:

Floral diagram of Asteraceae:

Economic importance of Asteraceae:

1. Food: Some plants in this family are used as food. Some of these are lettuce roots and leaves of cichory.

2. Medicinal: Artemisia yields a drug santonine. It is useful for round warms. Lettuce has properties resemble to opium.

3. Oils: Sunflower and Artemisia and many other species are cultivated for the extraction of oils. This oil is used as a cooking oil.

4. Dyes: The flower of Carthamus tinctorius yields a yellow dye.

5. Insecticide: The flowers of Chrysanthemum are grounded to produce a powder. It has an insecticide called Pyrethrum.

6. Poison: A large number of members of this family like rag weeds and golden rods cause hay fever. Certain plants are poisonous to livestock.

7. Ornamental plants: Many members of this family are cultivated as ornamental plants. These are sunflower, Chrysanthemum, Zinnia etc.

8. Weeds: Some plants of this family acts as weeds like Sonchus.

Distribution pattern of Asteraceae :

Asteraceae is the largest family of Angiosperms. It has more than 1000 genera and 93000 species. It is distributed in all parts of the world.

Common Species of Asteraceae :

1. Helianthus annuus, commonly known as Sunflower.

2. Lactuca sativa, commonly known as Lettuce.

3. Sonchus asper commonly known as Weeds.

4. Chrysanthemums indicus used for Salad.