It's been more than a century since the first Tex-Mex restaurant opened in Houston. George Caldwell brought The Original Mexican Restaurant to our city in 1907, influenced -- most agree -- by a restaurant of the same name in his hometown of San Antonio.

It would be another 20 years before Felix Mexican Restaurant opened on Lower Westheimer as one of the Tex-Mex restaurants that -- along with Ninfa's, Molina's and Leo's -- would define the genre in Houston. And it would take at least 40 more years before the cuisine had a definitive name: Tex-Mex, used to qualify a cuisine that neither purely Mexican nor purely Texan but an organic fusing of a blend of cultures throughout the region.

Diana Kennedy didn't see it that way, however, and the famous cookbook author dismissed Tex-Mex as Americanized Mexican food served at "so-called Mexican restaurants." This didn't sit well with Texans or Tejanos, who'd been serving what they simply referred to as "Mexican food" for decades.

"Texas-Mexican restaurant owners considered it an insult," wrote former Houston Press food critic Robb Walsh in his introduction to a six-part series on the history of Tex-Mex in 2000. To this day, you can usually bet that if a Texan says, "Let's go out for Mexican," you know they're talking about Tex-Mex.

Although Leo's and Felix are both closed now, Ninfa's is still recognized as the birthplaces of fajitas and Molina's as the standard bearer for the classic Tex-Mex dish of cheese enchiladas topped with chili con carne. And although Kennedy was initially dismissive of the genre, Tex-Mex is now considered to be America's first regional cuisine -- beloved not just in Texas, but throughout the world.

It's fajitas and enchiladas dishes that continue to define Tex-Mex cuisine in Houston, as much as frozen margaritas in Dallas, or the way the puffy taco symbolizes Tex-Mex in San Antonio. In compiling this list, I wanted to spotlight the 10 restaurants in Houston that preserve the standards of these beloved dishes -- the fajitas, the cheese enchiladas, the chili con queso, the margarita -- and serve as cultural touchstones for the history of the cuisine itself.