Which one is a kelp

Options

A. Batrachospermum
B. Ulothrix
C. Macrocystis
D. Dictyota.

Answer

To determine which option is a kelp, we will analyze each of the provided options based on their classification and habitat.

### Step-by-Step Solution:

1. **Understanding Kelp**:
- Kelp is a type of large brown algae that belongs to the order Laminariales. They are typically found in marine environments and form underwater forests known as kelp forests.

2. **Analyzing the Options**:
- **Option 1: Betulcospermum**:
- This is a type of red algae.
- It is found in freshwater environments.
- Since kelp is marine, this option can be eliminated.

- **Option 2: Eulothrix**:
- Eulothrix is classified as green algae.
- It can be found in both marine and freshwater environments.
- However, it does not belong to the kelp category, so this option can also be eliminated.

- **Option 3: Macrocystis**:
- Macrocystis is a type of large brown algae.
- It is indeed classified under the order Laminariales.
- This is a well-known genus of kelp that forms kelp forests in marine environments. This is our correct answer.

- **Option 4: Dictyota**:
- Dictyota is another type of brown algae.
- It is primarily found in marine conditions but belongs to a different order called Dictyotales.
- Thus, this option does not qualify as kelp.

3. **Conclusion**:
- After evaluating all options, the correct answer is **Option 3: Macrocystis**, as it is the only one that fits the definition of kelp.

### Final Answer:
**Macrocystis**