Xerophytes are a specific group of plants that have adapted to survive in arid and dry conditions. These plants are commonly found in regions with low water availability, such as deserts, semi-arid steppes, and other similar environments.

Option 1, tropical rainforest, is incorrect. Xerophytes are not typically found in tropical rainforests, as these regions receive abundant rainfall and have high humidity, which is not suitable for xerophytic plants.

Option 2, humid micro-thermal climate, is also incorrect. Xerophytes are specifically adapted to dry and arid climates, not humid climates.

Option 3, semi-arid steppes, is the correct answer. Xerophytes are abundant in semi-arid steppes, which are characterized by moderate rainfall and insufficient moisture for typical plant growth.

Option 4, tundra region, is incorrect. The tundra region is a cold and treeless area with a short growing season, and xerophytes are not generally found in this type of environment.

In conclusion, xerophytes are class of vegetation found in semi-arid steppes, where they have developed specialized adaptations to cope with limited water availability