Reed-swamp stage is characterised by the occurrence of :

Options

A. Free floating plants
B. Floating leaved plants
C. Submerged plants
D. Emergent plants

Answer

### Step-by-Step Solution:

1. **Understanding Reed Swamp Stage**: The reed swamp stage is a specific ecological stage that occurs in the hydrosphere, particularly in newly formed ponds or lakes.

2. **Characteristics of Reed Swamp**: This stage is characterized by the presence of biotic communities that develop in these aquatic environments. The plants in this stage are adapted to both submerged and aerial conditions.

3. **Plant Structure**: In the reed swamp stage, the plants have roots that are submerged in water while the upper parts of the plants are either floating on the water surface or are aerial. This adaptation allows them to thrive in such environments.

4. **Habit of the Plants**: The plants in the reed swamp stage are described as amphibious, meaning they have parts that are both submerged in water and parts that are above water.

5. **Examples of Plants**: Common examples of plants found in the reed swamp stage include Typha (commonly known as bulrush or cattail) and Cyperus (a type of sedge). These plants exemplify the characteristics of the reed swamp stage.

6. **Analyzing Options**: When considering the options provided:
- Free floating plants: Incorrect, as these do not have submerged roots.
- Floating leafed plants: Incorrect, as they do not fit the description of having both submerged and aerial parts.
- Submerged plants: Incorrect, as these are entirely underwater.
- Emergent plants: Correct, as these plants have parts that emerge above the water while their roots are submerged.

7. **Conclusion**: Therefore, the reed swamp stage is characterized by the occurrence of **emergent plants**.