Lunaria annua - Honesty.

The plant is familiar to most of us, unusually most of us find it more attractive when dead than alive.

If you are into plants you may enjoy this Blog.

Honesty is a member of the cabbage family, Brassicaciae, whose members typically have four petals arranged in a cross (explaining for the old name of the family, Cruciferae). The purple flowers of honesty aren't especially attractive, unless you happen to be an orange tip butterfly. (shameless plagiarism)