Every spring I'm stumped by this small flower that blooms in lawns, fallow gardens and waste places. With four petals and alternate "divided" leaves I could tell it's in the Mustard family. When I keyed it out in Newcomb's Wildflower Guide I arrived at Pennsylvania bittercress (Cardamine pensylvanica*).
But that's not what it is. It grows too well in poor soil to be a plant known for preferring wet habitats, swamps and stream banks. I began to suspect it's an alien.
Based on that hunch I sent photos to friends. Mark Bowers answered that this is hairy bittercress (Cardamine hirsuta), native to Europe and Asia.
Like Pennsylvania bittercress, its young leaves can be used in salads and are said to taste like radishes.
(photo by Kate St. John)
* Not a typo, the person who classified Cardamine pensylvanica omitted the second 'n' in our state's name.