pulvinus
1. A swelling at the base of a petiole or pinna, made up of cells that are capable of moving water in and out of their vacuoles quickly, resulting in movement of the petiole or pinna.

2. A thickened region at the node of a grass stem, often containing an intercalary meristem, which can raise the culm after lodging.

pulvinus A group of cells at the base of a leaf or leaflet in certain plants that, by rapidly losing water, brings about changes in the position of the leaves. In the sensitive plant (Mimosa pudica), the pulvinus is responsible for the folding of the leaves that occurs at nightfall or when the plant is touched or injured. See motor cell.

pulvinus In insects, a spongy pad between the front of the head and the mouth.