The Sierra Club endorsed Del. Heather Mizeur in the race for governor Monday, the first major environmental group to back a candidate in the contest.While Lt. Gov. Anthony Brown has dominated the endorsements in the heated Democratic primary campaign, Mizeur has recently picked up some coveted backers, including the Sierra Club.Mizeur, a Montgomery County Democrat, has also collected the backing from women's groups, including EMILY'S list and the political action committee of the Maryland National Organization for Women.&quot;Heather isn't afraid to speak her mind and stand up to special interests,&quot; Josh Tulkin, state director of the Sierra Club Maryland Chapter, said in a statement.Attorney General Douglas F. Gansler is also in the Democratic race to succeed Gov. Martin O'Malley, who is term-limited. The primary is June 24.