The correct answer is option 'A) Dichotomous branching'.

Riccia is a genus of liverworts, which are small, non-vascular plants that belong to the division Marchantiophyta. Riccia has a unique growth habit known as the rosette habit, which is characterized by the arrangement of thallus (body) in a circular or semi-circular shape.

Let's understand why the rosette habit of Riccia is due to dichotomous branching:

1. Definition of Dichotomous Branching:
- Dichotomous branching refers to the type of branching where the main axis repeatedly divides into two equal branches.
- Each division occurs at the node, resulting in a fork-like appearance.

2. Rosette Habit of Riccia:
- In Riccia, the thallus grows in a flat, ribbon-like structure.
- The thallus is composed of a single layer of cells, which are arranged in rows.
- The rows of cells are connected by cross walls, forming compartments.
- The growth of the thallus occurs by cell division at the apical meristem, which is located at the growing tip of the thallus.

3. Dichotomous Branching in Riccia:
- The growth of the thallus in Riccia is primarily due to dichotomous branching.
- At the apical meristem, the main axis of the thallus divides into two equal branches.
- This division results in the formation of two new tips, which can further divide in the same manner.
- The process of dichotomous branching continues, leading to the formation of a circular or semi-circular arrangement of the thallus.

4. Advantages of Rosette Habit:
- The rosette habit allows Riccia to efficiently capture sunlight for photosynthesis.
- The circular or semi-circular arrangement of the thallus ensures that all cells have access to light, maximizing the plant's ability to produce energy.
- The rosette habit also helps in the efficient absorption of water and nutrients from the environment.

In conclusion, the rosette habit of Riccia is due to dichotomous branching. This unique growth pattern allows Riccia to optimize its exposure to sunlight and efficiently obtain water and nutrients.