The sequence of communities of primary succession in water is

Options

A. (a) phytoplankton, sedges, free-floating hydrophytes, rooted hydrophytes, grasses and trees
B. (b) phytoplankton, free-floating hydrophytes, rooted hydrophytes, sedges, grasses and trees
C. (c) free-floating hydrophytes, sedges, phytoplankton, rooted hydrophytes, grasses and trees
D. (d) phytoplankton, rooted submerged hydrophytes, floating hydrophytes, reed swamp, sedges, meadow and trees.

Answer

### Step-by-Step Solution:

1. **Understanding Primary Succession in Water**:
- Primary succession in aquatic environments is known as hydrach. It refers to the gradual process of change in the species structure of a community in freshwater bodies as they transition to land.

**Hint**: Remember that hydrach is specifically related to freshwater ecosystems.

2. **Starting Point - Phytoplanktons**:
- The first community in hydrach is composed of phytoplanktons. These are microscopic organisms that float in the water and are the initial colonizers of the aquatic environment. An example of phytoplankton is *Chlamydomonas* or *Volvox*.

**Hint**: Think of phytoplanktons as the pioneers in the aquatic environment.

3. **Submerged Plant Stage**:
- After phytoplanktons, the next stage is the submerged plant stage. Here, rooted aquatic plants begin to establish themselves. Common examples include *Hydrilla* and *Valisneria*.

**Hint**: Submerged plants are those that grow completely underwater.

4. **Floating Plant Stage**:
- Following the submerged plants, the community transitions to the floating plant stage. This stage includes plants that float on the water surface, such as *Lemna* (duckweed) and *Pistia* (water lettuce).

**Hint**: Floating plants are crucial for providing habitat and shade in the water.

5. **Reed Swamp Stage**:
- The next community is the reed swamp stage, characterized by the presence of reed-like plants. These plants begin to grow in shallower waters, indicating a decrease in water dependency.

**Hint**: Reed swamps are often found at the edges of water bodies.

6. **Marsh Meadow Stage**:
- As succession continues, the marsh meadow stage appears. This stage features a mix of aquatic and terrestrial plants, such as *Cyperus* (sedge) and *Typha* (cattail).

**Hint**: Marsh meadows are transitional zones between water and land.

7. **Scrub or Woodland Stage**:
- The next stage is the scrub or woodland stage, where initial terrestrial plants start to dominate. This stage includes shrubs and small trees, indicating further reduction in water levels.

**Hint**: Scrub stages are characterized by the presence of woody plants.

8. **Climax Community - Forest Formation**:
- Finally, the climax community is reached, which is a mature forest ecosystem. This stage is characterized by a stable community of trees and other plants that thrive in the now established terrestrial environment.

**Hint**: The climax community represents the final and stable stage of succession.

### Conclusion:
The sequence of communities in primary succession in water (hydrach) is:
1. Phytoplanktons
2. Submerged plants
3. Floating plants
4. Reed swamps
5. Marsh meadows
6. Scrub/woodland
7. Climax community (forest)

The most appropriate answer to the question is option D, which correctly outlines this sequence.