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Hackberry (Celtis occidentalis)

Posted: October 13, 2016

This article is the last from William C. Paxton, our dendrology specialist, after his passing this past April. We hope you've enjoyed learning from Bill's spirit of inquiry about all things woods!
Hackberry Bark. Photo by W. Paxton 2015

Hackberry Bark. Photo by W. Paxton 2015

We were searching a pipeline in Greene County on a hot and muggy day, when all of a sudden we were approached and fed upon by a formidable flight of hungry butterflies. They craved the salt from our sweaty backs and shoulders, and we had a great photographic moment.

The species was the Tawney Emperor or Hackberry butterfly (Asterocampa clyton). The larvae food plant of these brown and golden flying wanderers is strictly hackberry.

This phenomenon soon pointed out that we were in the midst of a forest type that no US Forest Service silviculturalist ever put on a chart. It was an area of about seven acres of mixed hackberry and honeylocust (Gleditsia triacanthos). More normally, hackberry is found as single trees or scattered groupings throughout Pennsylvania woodlands.

It is readily identified by its never-to-be-forgotten bark (see photo). On smaller trees it is in deep singular rivulets that seem to have been artistically carved. While chestnut oak has deep bark furrows and black gum on older trees can become quite “chunky,” the bark ridges on hackberry seem to have almost been carefully glued into place.

It was always easy to identify larger hackberries by a profusion of witches’ brooms. Until white mulberry started to show the same broom collections, there was little doubt about hackberry identity from a distance.

This tree has been in the elm family since first named since the leaves do resemble the various elm species (even though in some cases the leaves seem to be three-veined from the base). I won’t tell you where the DNA studies wish to move it. If you are a wood technologist and look at a polished cross section with a ten-power lens, the summerwood looks very much like elm.

The tree becomes quite large with a spreading crown when open grown. The fruits are a dark blue drupe (single seed), which are eaten with relish and widely disseminated by bird species. Hackberry has the capacity to live in difficult environments and withstand the rigors of roadsides and industrial stressors, but they are more at home on the deep soil of gently sloping, well-drained uplands.

Now for the deeper thought. I did see and identify what they call sugarberry in southern Florida. Texts list a number of varieties and cultivars occurring in one form or another. This plant has found niches where it lives in profusion or rarity throughout the world. I wonder, are the butterflies the same species?