Plant Diversity III: Evolution of Seed Plants

Introduction

This chapter explores the evolutionary innovations that have enabled seed plants to dominate terrestrial ecosystems. It covers the adaptations of seed plants, their reproductive cycles, and the diversity and significance of gymnosperms and angiosperms.

Adaptations of Seed Plants

Key Innovations in Seed Plants

Seed plants possess several adaptations that have contributed to their evolutionary success and widespread distribution.

• Seeds consist of an embryo and stored nutrients, encased in a protective coat, allowing for survival and dispersal over long distances.

• All seed plants exhibit reduced gametophytes, heterospory, ovules, and pollen.

• Adaptations such as protective coats and reduced gametophytes help plants cope with terrestrial challenges, including UV radiation and desiccation.

• Water is not required for fertilization in seed plants, unlike in many non-seed plants.

Advantages of Reduced Gametophytes

Life Cycle Dominance and Protection

Seed plant life cycles are dominated by the sporophyte generation, with gametophytes being microscopic and protected within the tissues of the parent sporophyte.

• Gametophytes develop from spores retained within sporangia, shielding them from environmental stress and providing nutrients from the parent plant.

• This adaptation increases the survival rate of gametes and young embryos.

Comparison of Plant Life Cycles

*Additional info: Table reconstructed and expanded for clarity based on standard textbook comparisons of plant life cycles.*