What a treat this one is! This native loosestrife has a naturally occuring variation that gives the fine, lance-shaped foliage a lovely burgandy coloration.  Interestingly, Lysimachia is the host plant for a very special bee genus, Macropis. These tiny bees use the fragrant oil produced by the flowers to line their nests and feed the larvae after hatching. 
 
No need to be concerned about this being invasive, this species will spread to form a small colony, but it is not related to the terribly invasive "purple loosestrife" (which isn't really a loosestrife anyway!)