I plant arugula in the fall in every cold frame I can. Sometimes it languishes during the winter, but when it really gets going in the spring, it really gets going.
I generally let them bolt and go to seed because they self sow nicely and will come up in every nook and cranny and shady spot in the garden - and we eat it all.
Arugula is in the Cruciferae family - you can tell by the flowers: four petals in a cross shape. [Cresses and mustard are, too.] They are a part of the brassica family and the only brassica that I can grow reliably without cabbage worms bothering them. We've never seen a single cabbage worm on them ever.
I like the flowers. They're pretty and just as tasty as the leaves in salads.