The correct answer is option 2: Xerophytes. Xerophytes are plants that have adapted to survive in dry environments with limited water availability. They have special adaptations that help them conserve water, such as having thick waxy leaves to minimize water loss through evaporation and deep root systems to access groundwater. Xerophytes are typically found in desert and arid regions where water stress conditions are common.

Epiphytes, option 1, are plants that grow on other plants but do not rely on them for nutrients. They can be found in a variety of habitats, including rainforests and deserts, but their growth is not specifically associated with water stress conditions.

Heliophytes, option 3, are plants that require full sun exposure for photosynthesis. They can tolerate a range of water availability conditions and are not necessarily associated with water stress.

Sciophytes, option 4, are plants that prefer shade or low light conditions. They are not specifically adapted to thrive in water stress conditions.

Therefore, the correct answer is option 2: Xerophytes.