The Greenhouse: black walnut or tree of heaven?

We return to the greenhouse, my favorite place on earth after Dog Beach. What little I remember of trees tells me that the fast-growing tree below, the one so anxious for light and air it shattered a glass pane is either Juglans nigra (black walnut) or Ailanthus altissima (tree of heaven).

Juglans is a native of North America, once common to the forests of the northeast. Here’s what Edward Sibley Barnard says in New York City Trees: A Field Guide for the Metropolitan Area (Columbia University Press):

“Intolerant of shade, the black walnut secures its ecological niche by producing substances that retard the development of other trees around it. The black walnut was once plentiful in the eastern United States, but almost all the great old-growth forests are gone now, felled by lumberman seeking America’s finest cabinetry wood. ”

You might find this tree for sale in a nursery.

The other option, Ailanthus, is a weed tree imported from Asia either unwittingly or on purpose. It does not appear in Barnard’s guide, although you will find it everywhere, growing through cracks in sidewalk or old buildings. If you break a branch or a leaf, tree of heaven oozes a milky white stinky sap. The tree “suckers,” meaning that it’s roots shoot out sideways underground. If you cut down the tree or if the trunk is merely damaged, another will soon pop up nearby from the root system.

The tree above could very well be Ailanthus, on its quest to choke out all other plant life.