Lemon is a species of evergreen citrus—so their leaves are present and easily identifiable on the tree year round. Lemon trees share leaf characteristics with other citrus species but do have some slight distinctions that help you determine lemon leaves from others. Lemon leaves and branches are also cultivated for sale and use in the cut-flower trade as popular filler greens, making them even more recognizable and familiar than the leaves of other citrus species.
Look for dark- to medium-tone green leaves with a smooth, slightly glossy finish on the top side and a lighter-hued matte underside.
Identify lemon leaves by their shape and size: an elongated oval or elliptical typically 2 1/2 to 4 1/2 inches in length along the central vertical axis.
Feel around the edge or margin of the leaf, as lemon leaves will be lightly serrated with fine-pointed teeth that are sometimes readily visible to the eye.
Observe the leaf, looking for small, winged green sub-leaves near the petiole, where the lemon leaf connects to the stem that then connects it to the branch.
Observe the veining of the leaf, as lemon will have a central vertical vein larger than the other veins that splay out from the central vein and run almost to the edges of the leaves. The veins will appear lightly concave on the leaf surface and slightly convex on the underside.