They Fold Their Leaves | Outside My Window


Black locust, young leaves (photo from Wikimedia Commons)

Now that black locusts (Robinia pseudoacacia) are leafing out in Pittsburgh we can watch their leaves do exercises.

According to Wikipedia black locust leaves fold together at night and during wet weather, a trait of the Legume family called nyctinasty. I’ve often seen nyctinasty in clovers but have never noticed it in black locusts because I haven’t been paying attention. This month I plan to take a look.

It will be a good week to get close to black locusts. They’re blooming now with a sweet grape-like scent. See photos and read more about them in last year’s article: The Sweet Smell of Trees.