Nyctinastism

Part of speech: noun

Definitions

1. The movement or reorientation of plant leaves or flowers that occurs in response to the onset of darkness or nighttime conditions
2. The phenomenon involving the bending or movement of plant structures as they react to the arrival of night or reduced light exposure
3. A biological response in which certain plants adjust their orientations or positions in response to diminishing daylight or darkness

Etymology: "Nyctinastism" is a plain technical coinage built from Greek pieces. Its first part, "nycti-", comes from Greek "nyktos", meaning "of the night" or "night", the same root behind words like "nocturnal." The middle element, "-nast", comes from Greek "nastos", meaning "pressed close" or "compressed," and the ending "-ism" marks a process or phenomenon. Together they name the way certain plants, such as clover and bean plants, fold or droop their leaves at nightfall and open them again at dawn. The "-nast" piece is the most telling part. It derives from a Greek verb sense of pressing tightly, and it was chosen to describe a movement that is a response to the stimulus of darkness rather than a simple bending toward or away from something. Botanists used the same building blocks for related terms, so the word reads as a deliberate scientific label rather than a term that grew up in everyday speech.