[pauljz]

This isn't a totally new phenomenon either. I used to ride this stretch of the Metro to work every day back in 2009-2012, and I remember seeing these plants back then too. At the time they hadn't really taken hold at Cleveland Park, but Woodley Park was overrun with them.

These stations also had a tendency to flood during particularly heavy rains, so it's no surprise that questionable drainage is the culprit.

It's interesting to note that these stations get no natural light where the ferns are growing. It's all manmade light.