A native tree I'd never met

This spring I came upon a tree I didn’t recognize in my Philadelphia neighborhood. It was pumping out a sweet smell from showy flowers, and it grabbed my attention. When I find a tree I can’t identify in the city, I usually assume it’s an ornamental species that’s been imported from another country. That’s pretty common. Who doesn’t want to plant something exotic that none of the neighbors have? But in this case, my assumption was wrong. American yellowwood, Cladrastis kentukea in Latin, is a species native to the United States! How could I have missed such a distinctive tree?

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It turns out that American yellowwood has a very restricted natural range. Historically, it has been found only in small pockets and rocky areas in Kentucky or Tennessee and a few neighboring states. When we try to understand what makes a tree species tick, we often read a lot into its native range. But I’m not sure what has limited the distribution of this medium sized tree. It could be that its seeds don’t disperse well into new areas, or maybe it can’t compete with other species during the intense period that is tree adolescence.

Yellowwood is a legume, which means it’s in the same family as peas. If you’ve ever grown peas or beans in your garden, the shape of the little flowers in these hanging, white clusters will look familiar. I thought this might mean that yellowwood trees have the special ability to harvest nitrogen, like peas do, but it sounds like they didn’t inherit this family trait. Yellowwood do have seeds that grow in pods, just like peas. You can see some of the pods below. Both the flowers and the seeds appear in abundance every few years. Next time I get asked for a tree recommendation for someone’s yard, it’s going to be yellowwood!