Money Plant (Lunaria annua) is an easy-to-grow biennial that is called many names, including Dollar Plant, Silver Dollars, Honesty Plant, and Moonwort.
Not so rare, but very unusual.
This plant grows to just over two feet high and has large, dark green, heart-shaped leaves with pronounced serrated edges. Money Plant blossoms very early in the spring. Each flower has four petals and can be shades of reddish-purple or white. After the flowers fade, the plant forms seed pods that eventually become the shape and size of silver dollars. The seed pods start out green and become silvery, and after they dry they become so transparent you can see the dried seeds inside. Fabulous for to use in flower arrangements.
The Money Plant drops its seeds and reseeds readily, so if you have them growing in an undisturbed area, they will keep producing flowers and seed pods year after year.