The tree lilac (Syringa reticulata) is a Japanese cousin of the more familiar shrub lilac. It grows to be an actual tree 20 to 30 feet high, with an oval or spreading crown, whereas shrub lilacs top out at about 12 feet.
Bark and Flowers
The tree lilac's bark resembles cherry tree bark: satiny brown or red-brown, marked with prominent horizontal slits called "lenticels." Although on older trees the trunk may become gray and scaly, the younger branches will have the glossy bark. Tree lilac also produces creamy white, fragrant plumes of flowers in early summer. Their fragrance is more like privet than shrub lilac--sweet but musty.
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For the 2 weeks when it is in bloom, the flowers are the easiest way to identify tree lilac; there aren't many trees with plumy, fragrant, creamy flowers. When it is not in bloom (most of the year), the bark is an excellent identifier. A tree with glossy, satiny brown bark is most likely either a cherry or a tree lilac.
To distinguish between cherries and tree lilacs, look to the leaves. Cherry trees have "alternate leaves," meaning the leaves grow singly on alternate sides of the branch, one on the right, the next one a little higher on the left, all the way up the branch. But tree lilacs have "opposite leaves," meaning they grow in pairs, directly opposite each other, along the branch.
Another difference between tree lilac and cherry leaves is that tree lilac leaves have smooth edges, where cherry leaves are usually lightly serrated.
Individual tree lilac leaves are 2 to 5 inches long and about half as wide, dark green above and grayish green below. They are roughly tear-drop shaped, rounded near the stem and with a long "drip tip" at the other end.