Regency Centers Corp. (NYSE:REG) and Equity One, Inc. (NYSE:EQY) have agreed to combine to form one of the largest shopping center REITs in the country with a portfolio of primarily grocery-anchored properties, jumping ahead of rivals Kimco and Federal Realty with a total market capitalization expected to exceed $15.6 billion.

The merger, which was announced by the two companies Monday evening, will create a national shopping center owner and…