Leaves Leaves are the main photosynthetic organs of a plant. A leaf usually exists in the shape of a flattened blade which is joined to the node of a stem by a petiole . Monocot leaves have parallel major veins running the length of the blade. Dicot leaves have a multi-branched network of major veins. Can be palmate or pinnate .
All leaves have numerous minor cross-veins.
Plant taxonomists use a variety of leaf characteristics to classify plants.