Wildflowers: What is this plant - Western PA?

These upright plants are about 1 foot tall and growing in a Western PA lawn. They have shallow roots, very small 4 petal white flowers, narrow opposite leaves and prominent upright seed pods. First noticed them in Mid-March.

Thanks

 

Cardamine.

 

Thanks, nice to have it confirmed. From my research I thought it might be a bittercress, but wasn't sure since the upper and lower leaves were different. It's common name is Pennsylvania bittercress.

Before I posted, I didn't realize there was another thread here that discussed the same plant:
http://www.botanicalgarden.ubc.ca/forums/showthread.php?t=72579