What's the difference between Petite Sirah and Durif—or is there one?

Hello there! I'm Dr. Vinifera, but you can call me Vinny. Ask me your toughest wine questions, from the fine points of etiquette to the science of winemaking. And don't worry, I'm no wine snob—you can also ask me those "dumb questions" you're too embarrased to ask your wine geek friends! I hope you find my answers educational, empowering and even amusing. And don't forget to check out my most asked questions and my full archives for all my Q&A classics.
Dear Dr. Vinny,
I’ve been reading a lot about Petite Sirah and Durif. What does the latest research finally say? Am I drinking Durif or Petite Sirah or a combination of other stuff as well?
—Jon, Manteca, Calif.
Dear Jon,
"Petite Sirah" is the name Americans call the Durif grape. There are actually two different spellings of the variety—Petite Sirah, which is mostly widely used, and Petite Syrah, which is a bit of a throwback version, and unfortunately complicates the perception of Petite Sirah and Syrah being the same grape.
Durif has a strange history. In the 1880s, French botanist François Durif crossed the Syrah and Peloursin grapes—some suspect by accident—to create Durif. But despite its origins being in France, it never really took off there—it’s practically nonexistent in the country today. But it thrived in California, where it has a strong following, and later it spread modestly to other parts of the world.
—Dr. Vinny