Kingdom Plantae

Introduction to Seed Plants

Seed plants, or Spermatophytes, are a major group within the plant kingdom characterized by their ability to reproduce via seeds. This adaptation has allowed them to dominate terrestrial ecosystems since their origin approximately 360 million years ago.

• Spermatophyte: Plants that reproduce by seeds, providing protection and nourishment to the developing embryo.

• Seedless vascular plants: Earlier-evolved plants (e.g., ferns) that reproduce via spores rather than seeds.

• Seed plants are divided into two main groups: Gymnosperms and Angiosperms.

Additional info: Seed plants have complex vascular tissues (xylem and phloem) for efficient transport of water, minerals, and nutrients.

Classification of Seed Plants

Main Groups of Seed Plants

Seed plants are classified based on the presence or absence of fruit covering the seed.

• Gymnosperms: "Naked seed" plants; seeds are not enclosed within a fruit.

• Angiosperms: "Flowering plants"; seeds are enclosed within a fruit, which develops from the ovary after fertilization.

Comparison: Gymnosperms vs. Angiosperms

The following table summarizes the key differences between gymnosperms and angiosperms:

Evolution and Diversity of Seed Plants

Origin and Adaptation

Seed plants first appeared in the late Devonian period, about 360 million years ago. Their evolution marked a significant advancement over seedless plants, allowing for greater survival and dispersal in various environments.

• Tracheids: Specialized water-conducting cells found in vascular plants, including seed plants.

• Seed plants diversified into multiple phyla, including Coniferophyta (conifers), Cycadophyta (cycads), Ginkgophyta (ginkgo), and Gnetophyta (gnetophytes).

Additional info: The development of seeds allowed plants to colonize drier habitats and provided a protective structure for the embryo during unfavorable conditions.

Structure of Seeds and Reproductive Organs

Seed Anatomy

Seeds consist of three main parts:

• Embryo: The young plant that will develop after germination.

• Endosperm: Nutritive tissue that supports embryo development (especially in angiosperms).

• Seed coat: Protective outer layer derived from the integument.

Reproductive Structures

• Gymnosperms: Produce seeds on the surface of cone scales; lack flowers and fruits.

• Angiosperms: Produce seeds within ovaries, which mature into fruits; have complex flowers for reproduction.

Additional info: Angiosperms exhibit double fertilization, resulting in both embryo and endosperm formation.

Examples and Applications

Representative Seed Plants

• Pine (Pinus): A typical gymnosperm with needle-like leaves and woody cones.

• Orchid, Sunflower: Examples of angiosperms with diverse flower structures and fruit types.

Seed plants are essential for terrestrial ecosystems, agriculture, and human society, providing food, timber, medicines, and oxygen.

Key Terms and Definitions

• Spermatophyte: Seed-producing plant.

• Gymnosperm: Plant with naked seeds, not enclosed in fruit.

• Angiosperm: Flowering plant with seeds enclosed in fruit.

• Tracheid: Water-conducting cell in vascular plants.

• Endosperm: Nutritive tissue in seeds of angiosperms.