The Macerich Co. has rejected a hostile offer from Simon Property Group Inc., the largest shopping mall owner in the country, to buy it in a stock and cash deal valued at $91 per share, or $22.4 billion.

Macerich said today in a release that its board rejected the offer, saying that it undervalues the company.

After making the offer on March 9, Simon said it had entered into a deal to sell some Macerich shopping centers to General Growth Properties Inc., the nation’s second largest mall owner. Macerich is No. 3.

The California-based company has adopted a “poison pill” defense to defend against a takeover in the form of a limited-duration shareholder rights plan, which becomes effective today and would expire at the company’s annual meeting in 2016.

The rights become exercisable if any person or group acquires beneficial ownership of 10 percent or more of Macerich’s common stock. Simon said in November that it has a 3.6 percent stake in Macerich.

The Macerich board also created a new classified board structure that it will review next year.

Des Moines natives Art and Ed Coppola were among the founders of Macerich. Art Coppola is its chairman and CEO. His brother, Ed, is president. Greater Des Moines businessman Fred Hubbell is a director. Southridge Mall has been owned at various times by General Growth and a partnership of Macerich and Simon.