I've found my plans and plants

As kids we called them Moon pennies, not sure why though.

Well, Lunaria is its botanical name and Moonwort is one of its English names, both because of the seed pods. I guess the "pennies" bit is similarly descriptive.

Ooh just checked Wikipedia, it says "Lunaria, common names honesty, dollar plant, money-in-both-pockets, money plant, moneywort, moonwort, and silver dollar". Never heard of most of those. You should update it with Moon pennies for other people who look it up!