My parents had these plants pop up in their gardens this year and they have NO idea where they came from. We've never seen anything like it around here.

They have very thick main stalks, at least 1" + in diameter. They are tall and had small yellow flowers, and now seedpods.

Here's a photo of one that was cut down and is lying on the driveway. I have additional photos if you think they're necessary. Does anyone know what they are?

{{gwi:332509}}