Selaginella and Salvinia are considered to represent a significant step toward evolution of seed habit because

Options

A. female gametophyte is free and evolution dispersed like seeds
B. female gametophyte lack archegonia
C. megaspores posses endosperm and embryo sourrounded by seed coat
D. embryo develops in female gametophyte which retained on parent sporophyte

Answer

**Step-by-Step Solution:**

1. **Understanding the Organisms**: Selaginella and Salvinia are types of pteridophytes, which are vascular plants that reproduce via spores rather than seeds.

2. **Life Cycle Comparison**: The life cycle of pteridophytes differs from that of bryophytes (mosses and liverworts) and higher plants (gymnosperms and angiosperms). In bryophytes, the gametophyte generation is dominant, while in angiosperms, the sporophyte generation is dominant.

3. **Independent Phases**: In pteridophytes, both the gametophyte and sporophyte phases are independent of each other. This is a key characteristic that sets them apart from bryophytes and higher plants.

4. **Heterospory**: Selaginella and Salvinia are heterosporous, meaning they produce two types of spores: megaspores (female) and microspores (male). This is an important evolutionary step towards seed formation.

5. **Development of the Embryo**: A significant aspect of Selaginella and Salvinia is that the embryo develops within the female gametophyte, which is retained on the parent sporophyte. This retention is a critical step towards the evolution of seed habit.

6. **Significance of Retention**: The retention of the female gametophyte on the sporophyte allows for better protection and nourishment of the developing embryo, which is a precursor to seed development in higher plants.

7. **Conclusion**: Therefore, Selaginella and Salvinia represent a significant evolutionary step towards the seed habit due to the retention of the female gametophyte on the parent sporophyte and the development of the embryo within it.

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