Plants without well-differentiated stem, root, and leaf are kept in ___.

Thallophyta:

1. Thallophyte is the most basic plant with no well-differentiated body structure.
2. They are typically found in damp or wet environments.
3. This is because of the absence of "true roots" and vascular systems, which are required for water and mineral transfer.
4. As a result, they are seen in damp or wet environments.
5. Generally, their reserve food is starch.
6. They are generally autotrophic.
7. The majority of this group produces their own food. However, other members, such as fungus, rely on other sources of nutrition.

Final answer: Plants without well-differentiated stem, root, and leaf are kept in Thallophyta.