Downward curvature caused by greater growth of upper surface of an organ.
The phenomenon of a petiole’s downward bending, resulting in an obtuse angle between its base and the stem, is referred to as “petiole nutation.” The orientation of the lamina, or blade of the leaf, may either be vertical with the apex hanging downwards, or it may follow the curvature of the petiole, causing the upper surface to face inward towards the stem. Despite this bending, the petiole and lamina maintain their turgidity, which differentiates this condition from wilting where the tissues become flaccid.