Which of the following is an aquatic fern and an excellent bio- Fertilizer ?

Options

A. Azolla
B. Salvinia
C. Marsilia
D. Pteridium

Answer

To solve the question "Which of the following is an aquatic fern and an excellent bio-fertilizer?" we will analyze each of the given options: Azolla, Salvinia, Marsilia, and Pteridium.

### Step-by-Step Solution:

1. **Identify the Options**: The options provided are:
- Azolla
- Salvinia
- Marsilia
- Pteridium

2. **Define Aquatic Ferns**: Aquatic ferns are ferns that grow in water or wet environments. They can float on the surface of water or grow submerged.

3. **Evaluate Each Option**:
- **Azolla**: This is a small aquatic fern that floats on the surface of water. It is known for its ability to fix nitrogen due to the presence of a symbiotic cyanobacterium (Anabaena). This makes Azolla an excellent bio-fertilizer.
- **Salvinia**: This is also a floating fern but is not recognized as a bio-fertilizer.
- **Marsilia**: This is a genus of aquatic ferns but does not have significant use as a bio-fertilizer.
- **Pteridium**: Commonly known as the Eagle fern, it is not aquatic and is not used as a bio-fertilizer.

4. **Conclusion**: Based on the evaluations, Azolla is the only option that is both an aquatic fern and recognized as an excellent bio-fertilizer due to its nitrogen-fixing capabilities.

### Final Answer:
The correct answer is **Azolla**.

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