What term is used to describe non-directional responses to a stimulus, often found in plants?

Nastic movements describe non-directional responses in plants that occur independently of the direction of the stimulus. This means the responses happen in a fixed, predictable manner, regardless of where the stimulus is coming from. An example of this would be the opening and closing of flowers or the folding of leaves in response to touch or changes in light. The key feature of nastic movements is their lack of directional growth toward or away from the stimulus, which distinguishes them from tropical movements, which are directional in response to environmental signals.

In contrast, tropism refers to growth responses where plants move toward or away from a directional stimulus, such as light or gravity. Kinesis is a type of movement in response to stimuli, but it is not specific to plants and does involve a change in activity rather than a growth response. Thigmotropism is a specific type of tropism involving growth in response to touch, showing directional behavior towards contact. Therefore, the term that accurately captures the essence of non-directional responses in plants is nastic movements.