A unifacial leaf that is flat in cross section due to a lamina that develops in a median plane (perpendicular to the axis), rather a transverse plane (tangent to the axis) throughout all of part of the length of the leaf.

Common in many monocots and some dicots. Note that ensiform leaves have two sides, but both sides arise from the same surface of the leaf meristem (abaxial or adaxial). In some leaves, the petiole may twist, giving the appearance that the lamina is ensiform, but it is not.