hyponasty

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The upward bending of a leaf or other plant part, resulting from greater growth of the lower side than of the upper side.

from The Century Dictionary.

• noun In botany, increased growth along the lower surface of an organ or part of a plant, causing the part to bend upward. Compare epinasty.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Bot.) Downward convexity, or convexity of the inferior surface.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun botany an upward bending of leaves or other plant parts, caused by increased growth on their lower surface