Define the part of the leaf labelled 'A' in the given image.
Lamina
The labelled part in the image is called leaf blade or lamina. The lamina is the broad, green part of the leaf that is exposed to sunlight. The midrib is a central, thick, linear structure that runs along the length of the lamina. Petiole is the stalk that supports a leaf in a plant and attaches it to the stem.