We introduce a new reference axis for leaf classification. The new reference axis, called a Mid-Leaf axis, is based on a quadratic curve that lies on the middle of a leaf. This curve is derived from three basic landmark points: an apex, a centroid, and a petiole. After mapping to a new plane based on this curve, leaf shape features are invariant under translation, rotation, scaling, and bending. We propose the leaf shape features based on partitioning the morphological features and the tangent’s direction angle of the leaf contour. Using the ImageCLEF2012 database (Scan-type only), our experimental results show that the proposed method outperforms the state-of-the-arts for leaf classification in the accuracy metric.