Common names for plants can be misleading, such as Jerusalem artichoke has nothing to do with that city or artichokes. But some can be right on, such as Aconitum or monkshood. Monkshood's flower shape resembles a helmet or a hooded cloak of a monk. It's also called wolfsbane for its ability to ward off werewolves, but that's another story.
Whatever you call it, monkshood is a hardy perennial flower that grows well in full or part sun and along the shore. I first noticed it years ago blooming in Bar Harbor, Maine so you know it's a tough plant.
Monkshood produces purple colored flowers in autumn when little else is blooming. It grows 3 to 4 feet tall, so it's good planted in clumps behind other fall bloomers such as sedum and asters. Bressingham Spire is a good purple variety, but there are other colors as well: Stainless Steel -- a blue flowered type, Pink Sensation -- a flashy pink bloomer, and Ivorine -- a white selection.
Monkshood likes a well-drained, moist soil, and doesn't appreciate hot, dry conditions especially in hot afternoon sun. The stems are sturdy, make great cut flowers, and don't need support. Although it's happiest if not moved frequently, you can divide it to make more plants every three to four years.
The one drawback to this perennial is that all parts of the plant are poisonous. In fact, in medieval times, it was often used to poison enemies or unfaithful spouses. So, be careful with animals and young children around and wear gloves when cutting it to keep the sap off any wounds and cuts.