These photos of Purple Deadnettle [Lamium purpureum] where taken at Fletcher Park on 16 March 2013. Newcomb’s Wildflower Guide, pages 86-87, says it’s a member of the mint (Lamiaceae) family that blooms Spring to Fall on roadsides and in waste places. It does have a square stem.
USDA Plant Listing:Lamium purpureum
Purple Deadnettle – 16 March 2013
Purple Deadnettle (close-up) – 16 March 2013