The black walnut (Juglans nigra) and the pecan tree (Carya illinoensis) are two nut-producing species suitable for large landscapes. The black walnut grows considerably smaller than the pecan, to about 75 feet; the pecan can stretch to heights well over 100 feet. Identify the black walnut and the pecan tree's foliage by its makeup, color, size and smell.
Black Walnut Leaf Identification
Count the number of leaflets on a single compound black walnut leaf. On this species, there are as many as 23 leaflets or as few as 13 growing on each leaf's central stem.
Measure the central stem of the compound leaf on a black walnut. The stems range from 12 inches in length to 24 inches. Measure the length of the individual leaflets. These are usually in the range of from 2 1/2 inches to 5 inches long.
Look at the shape of the black walnut leaflet. These leaflets are lance-shaped and have a series of serrations along their edges, with long points at their ends, according to the "National Audubon Society Field Guide to Trees: Eastern Region."
Examine the surfaces of the leaflets, looking for a soft covering of minute hairs on the undersides. The upper surface of the leaflet is smooth.
Observe the color of the black walnut leaflets. In spring and summer, the leaves are dark shades of green. In the autumn, they change to a dull yellow shade, notes the Missouri Botanical Garden.
Pecan Leaf Identification
Count the leaflets attached to the central stem of a pecan leaf. There are as many as 17 or as few as 11.
Measure the stem of a pecan leaf. Its size ranges between 12 inches and 20 inches. Each of the individual leaflets are from 2 inches in length to 7 inches long.
Observe the shape of each pecan leaflet. The leaflets have a shape similar to that of a sickle, curving and having a sharp point at their ends.
Inspect the color of pecan leaves, watching for the leaflets to be shades of greenish-yellow. The leaves turn a yellow tint in fall.
Crush the pecan leaflets with your fingers and smell them. The leaflets give off an odor that Floridata describes as disagreeable.