Seed plants

Seed plants or Spermatophytes are a group of plants that reproduce through the production of seeds, a significant evolutionary development from more primitive plants that reproduce via spores. Seed plants are divided into two main groups: the Gymnosperms and the Angiosperms. Gymnosperms, which include conifers, cycads, ginkgo, and gnetophytes, produce seeds that are not enclosed in an ovary. Angiosperms, or flowering plants, develop seeds within a protective structure known as a fruit.

Evolution

The evolution of seed plants marks a pivotal point in the history of plant life, enabling plants to colonize new environments and significantly diversify. The earliest known seed plants date back to the Devonian period, over 360 million years ago. The development of the seed, an embryonic plant enclosed in a protective outer covering, allowed plants to survive in a wider range of environments and conditions. This adaptability contributed to the dominance of seed plants in most terrestrial ecosystems.

Characteristics

Seed plants share several key characteristics:

• The production of seeds, which contain the embryo and a supply of nutrients surrounded by a protective coat.
• The presence of a vascular system, including xylem and phloem, for the transport of water, nutrients, and sugars throughout the plant.
• The development of roots, stems, and leaves, which facilitate nutrient uptake, support, and photosynthesis, respectively.
• In many seed plants, the presence of flowers or cones that facilitate reproduction.

Reproduction

Reproduction in seed plants involves complex life cycles that include both sexual and asexual phases. The sexual phase involves the production of male and female gametes, which can occur in the same or separate structures. In gymnosperms, male gametes are typically found in pollen grains, while female gametes are located in ovules. In angiosperms, both male (pollen) and female (ovule) gametes are produced in flowers. Fertilization occurs when a pollen grain reaches an ovule, leading to the development of a seed.

Classification

Seed plants are broadly classified into two major groups:

Gymnosperms

Gymnosperms are seed plants that do not produce flowers or fruits. Their seeds are often exposed on the surface of cone scales. Gymnosperms include four main groups:

• Coniferophyta (conifers)
• Cycadophyta (cycads)
• Ginkgophyta (ginkgo)
• Gnetophyta (gnetophytes)

Angiosperms

Angiosperms, or flowering plants, are the most diverse group of seed plants, with over 300,000 species. They are characterized by the production of flowers and fruits that contain seeds. Angiosperms are further divided into two groups based on the number of seed leaves (cotyledons) in the embryo:

• Monocotyledons (monocots), with one seed leaf
• Dicotyledons (dicots), with two seed leaves

Importance

Seed plants are of immense ecological and economic importance. They dominate most terrestrial ecosystems, providing habitat and food for a wide range of animal species. Economically, seed plants are a vital source of food, medicine, timber, and many other products essential to human life and industry.

Conservation

Many seed plant species are under threat from habitat destruction, climate change, and overexploitation. Conservation efforts are crucial to protect these vital resources for future generations.