Model Answer
0 min readIntroduction
Asteraceae, commonly known as the sunflower family or Compositae, is one of the largest families of flowering plants, boasting over 32,000 known species distributed globally. Characterized by its unique inflorescence – the capitulum – Asteraceae plays a crucial role in various ecosystems and holds significant economic importance for humans. From common wildflowers like daisies and sunflowers to economically vital crops like lettuce and safflower, the family’s diversity is remarkable. Understanding its botanical features is fundamental to appreciating its ecological and economic contributions. This note will comprehensively explore the defining characteristics of Asteraceae.
Morphological Characteristics
The most distinctive feature of Asteraceae is the capitulum, often mistakenly considered a single flower. In reality, it’s a dense cluster of numerous small, individual flowers called florets, arranged on a flattened or convex receptacle. Florets are of two main types:
- Ray florets: These are located on the periphery of the capitulum and typically have a ligulate (strap-shaped) corolla, often brightly colored to attract pollinators. They are usually sterile and function primarily in attracting insects.
- Disc florets: These are located in the central disc of the capitulum and have a tubular corolla. They are generally bisexual and fertile.
Leaves are typically alternate, simple, and often have a characteristic venation pattern. They can be entire, toothed, or lobed. Stems are often herbaceous, but some species exhibit woody growth. The root system is usually taproot, though fibrous roots are also common.
Anatomical Characteristics
Asteraceae exhibit several unique anatomical features:
- Pollen grains: Typically tricolpate (having three furrows or pores), a characteristic feature of eudicots.
- Vascular bundles: Often arranged in a ring within the stem, providing structural support.
- Laticiferous vessels: Many Asteraceae species contain laticiferous vessels that produce a milky sap (latex), containing various chemical compounds, some with medicinal properties.
Reproductive Characteristics
Reproduction in Asteraceae is primarily sexual, through pollination and seed formation. Pollination is often facilitated by insects, birds, or wind. The ovary is inferior, and the fruit is typically a dry achene, often with a pappus – a modified calyx that aids in wind dispersal. The pappus can take various forms, such as bristles, scales, or a ring.
Economic Importance
Asteraceae has immense economic importance, providing numerous benefits to humans:
- Oilseeds: Sunflower (Helianthus annuus) and safflower (Carthamus tinctorius) are major sources of vegetable oil.
- Food crops: Lettuce (Lactuca sativa), artichoke (Cynara scolymus), and endive are widely consumed as vegetables.
- Medicinal plants: Chamomile (Matricaria chamomilla) and echinacea (Echinacea purpurea) are used for their medicinal properties.
- Ornamental plants: Daisies, chrysanthemums, and asters are popular ornamental plants.
- Rubber source: Guayule (Parthenium argentatum) is a potential source of natural rubber.
- Insecticides: Pyrethrum (Chrysanthemum cinerariifolium) is a source of pyrethrins, natural insecticides.
Phylogenetic Relationships and Evolution
Asteraceae is a relatively young family, originating in the Cretaceous period (around 100 million years ago). Phylogenetic studies, based on molecular data, suggest that the family originated in the Laurasian landmass and subsequently diversified and spread globally. The evolution of the capitulum is considered a key innovation that contributed to the family’s success. The family is closely related to the Calyceraceae and Goodeniaceae families.
| Characteristic | Description |
|---|---|
| Inflorescence | Capitulum (head) – a dense cluster of florets |
| Floret Types | Ray florets (ligulate, sterile) & Disc florets (tubular, fertile) |
| Ovary Position | Inferior |
| Fruit | Achene, often with a pappus |
Conclusion
In conclusion, Asteraceae is a remarkably diverse and economically significant plant family, distinguished by its unique capitulum inflorescence and widespread distribution. Its evolutionary success can be attributed to the adaptive advantages conferred by its specialized floral structure and efficient dispersal mechanisms. Continued research into the family’s genetic diversity and ecological interactions is crucial for harnessing its potential for sustainable agriculture, medicine, and conservation.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.