A: Epiphyllous roots arise from the margins of leaf lamina.
R: Epiphyllous roots help in vegetative reproduction.

Answer

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that "Epiphyllous roots arise from the margins of leaf lamina."
- This is true as epiphyllous roots are specialized roots that emerge from the edges of the leaf's lamina, particularly in certain plants like Bryophyllum.

2. **Understanding the Reason**:
- The reason provided is that "Epiphyllous roots help in vegetative reproduction."
- This is also true because these roots allow the plant to reproduce asexually. When the leaf falls to the ground, the roots can anchor into the soil, allowing the leaf to develop into a new plant.

3. **Connecting Assertion and Reason**:
- Both the assertion and the reason are true, and they are related. The presence of epiphyllous roots enables the leaf to not only survive but also to propagate and grow into a new individual plant, thus facilitating vegetative reproduction.

4. **Conclusion**:
- Therefore, both the assertion (A) and the reason (R) are true, and the reason correctly explains the assertion.