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Common hackberry is a member of the Elm Family (Ulmaceae). It is a large deciduous tree reaching 12 m to 18 m in height at maturity. It typically lives to be 150 to 200 years old and exhibits its greatest annual growth between 20 and 40 years of age. The branches tend to droop, giving mature trees a cylindrical shape and the appearance of even and equal spread of branches

The bark of the hackberry has corky projections and is often called "warty". This texture is generally on the trunk and branches.

Celtis occidentalis has an alternate brancing pattern. There is no terminal bud and the branches usually are formed in a zig-zag pattern. It is apparently uncommon for twigs to be as straight as this one.

The photos above show a condition that is commonly called witches'-broom. It is characterized by a dense clustering of twigs. The cause of witches'-broom is not known for certain, but it is thought that it caused the interaction of an eriophyid mite and a powdery mildew fungus. These photographs are on a tree in parking lot 21, near the end of a row close to theThornhill building. The tree is identified as Celtis occidentalis 'Windy City'.

Hackberries are native to the flood plains of the eastern United States.

I don't know if all of these trees are hackberries, but the sign says "hackberries" and it does show their willingness to grow in this flooded area.

The fruit of the hackberry is a small berry that ripens in September or October. I did see some fruit on trees on December 30, 2008, but was so involved in taking photos of the flooding that I neglected to photograph the berries.

The first photo on left shows leaves in mid May. As the summer progresses, the leaves are likely to be covered with nipple galls. These are homes of small insects, named Hackberry psyllids. These are jumping plant lice that look like tiny cicadas. The tree isn't generally damaged by the galls, but they are unsightly.

Small, jumping plant lice

Lives on hackberry.  Adult psyllids are about 4 to 5 mm long, and look like miniature cicadas.  The tiny, yellowish nymphs rapidly become enveloped by gall tissue and are rarely seen.  Nipple galls are light green, nipple-shaped, and about 4 mm in diameter. 

Psyllids overwinter as adults in bark cracks and crevices.  After mating in spring, females lay eggs on new growth.  Nymphs feed on new growth all summer, causing galls to form on the underside of leaves.  In September, large numbers of adults emerge from galls and collect around doors and windows.

Insect injury occasionally causes premature leaf drop, but trees are not seriously damaged.