Which one of the following is not a homosporous fern ?

Options

A. Dryopteris
B. Pteris
C. Pteridium
D. Azolla

Explanation

To determine which of the following is not a homosporous fern, we need to understand the definitions of homosporous and heterosporous plants.

### Step-by-Step Solution:

1. **Understand the Definitions**:
- **Homosporous plants** produce only one type of spore, which can develop into a gametophyte that produces both male and female gametes.
- **Heterosporous plants** produce two types of spores: microspores (male) and megaspores (female).

2. **Identify the Options**:
- The options provided are:
- Dryopteris
- Pteridium
- Azolla

3. **Analyze Each Option**:
- **Dryopteris**: This is a genus of ferns that is known to be homosporous. It produces only one type of spore.
- **Pteridium**: Commonly known as the bracken fern, it is also a homosporous fern, producing only one type of spore.
- **Azolla**: This is a genus of aquatic ferns, commonly known as mosquito ferns, which is heterosporous. It produces both microspores and megaspores.

4. **Conclusion**:
- Since Dryopteris and Pteridium are both homosporous ferns, and Azolla is heterosporous, the answer to the question "Which one of the following is not a homosporous fern?" is **Azolla**.

### Final Answer:
**Azolla** is not a homosporous fern.