Vegetative propagatation in Pistia is a

Options

A. Underground stem
B. Subaerial stem
C. Underground root
D. Aerial stem

Answer

To determine the method of vegetative propagation in Pistia, we need to analyze the options provided and understand the growth structure of the plant.

### Step-by-Step Solution:

1. **Understanding Vegetative Propagation**: Vegetative propagation is a form of asexual reproduction in plants where new individuals arise from vegetative parts like stems, roots, or leaves.

2. **Identifying the Plant Structure**: In Pistia, the plant has a rosette of leaves that grow above the water surface, and it has roots that extend into the water or soil.

3. **Analyzing the Options**:
- **Option A: Underground Stem**: This refers to a stem that is completely below the soil surface. This does not apply to Pistia, as it does not primarily propagate through an underground stem.
- **Option B: Sub-aerial Stem**: This refers to a stem that is partially above and partially below the soil surface. In Pistia, the stem grows laterally just below the surface of the water or soil, which allows it to form new clusters of leaves and roots.
- **Option C: Underground Root**: This option refers to propagation through roots, which is not the case for Pistia.
- **Option D: Aerial Stem**: This refers to stems that are completely above the soil surface. While Pistia has aerial parts, it does not propagate through this method.

4. **Conclusion**: Given the structure of Pistia and how it propagates, the correct answer is **Option B: Sub-aerial Stem**. This method allows Pistia to spread and form new plants through offsets, which are new rosettes of leaves that develop from the sub-aerial stem.

### Final Answer:
**Option B: Sub-aerial Stem**