Fucus and Sargassum both shows heterothallic habit .

Answer

### Step-by-Step Solution:

1. **Understanding Heterothallic Habit**:
- Heterothallic plants are those where male and female reproductive organs are found on separate individuals. This means that one plant will produce only male gametes, while another will produce only female gametes.

2. **Identifying Fucus and Sargassum**:
- Fucus and Sargassum are types of brown algae. To classify them correctly, we need to determine whether they exhibit heterothallic or monoecious characteristics.

3. **Clarifying the Terms**:
- The term "dioecious" is synonymous with heterothallic, meaning that these plants have distinct male and female individuals.
- The term "monoecious" indicates that a single plant has both male and female reproductive systems.

4. **Analyzing the Reproductive Structures of Fucus and Sargassum**:
- Both Fucus and Sargassum are known to have both male and female reproductive structures on the same plant, which classifies them as monoecious rather than heterothallic.

5. **Conclusion**:
- Since Fucus and Sargassum do not exhibit heterothallic habits, the statement that they do is false.

### Final Statement:
Fucus and Sargassum do not show heterothallic habits; they are monoecious, meaning they have both male and female reproductive structures on the same plant. Therefore, the statement is false.

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