In my mind, Rioja is to Spain as Chianti is to Italy. If you asked most people to quickly name one wine from Spain and one from Italy, I would bet that a large majority would instantly name those iconic wines, and for good reason. Both areas have a long wine making history and are not only readily available in almost every shop that sells wine, but good bottles can be had for reasonable prices as well. They both also feature what might be considered each country's "star grape:" Tempranillo in Spain and Sangiovese in Italy.
Of course, the analogy isn't perfect. Chianti has much stricter regulations regarding what grapes in what proportions can go into its wines and still be eligible for the Chianti classification (there is also no white Chianti while Rioja allows for white wine production). There are regulations in Rioja also, but only for the allowed grape varieties, not the proportions (and even then I believe that wineries can appeal for special permission to include grapes like Cabernet Sauvignon). What this means is that it is possible to end up with a 100% varietal bottling from any of the approved red wine grapes within Rioja: Tempranillo, Garnacha (Grenache in France), Mazuelo and Graciano. Those first two grapes are familiar enough, and Mazeulo is the local term for Carignan, a grape grown in many regions all over the world, which brings us to Graciano.
Graciano is thought to be native to Rioja, where it is used to provide color and aroma to blended Rioja red wines (Oz Clarke's comparison to how Petit Verdot is used in Bordeaux is an enlightening analogy). Typically, it makes up less than 15% of the blend when it is used at all. It can also be found in neighboring Navarra. Graciano was once very widely grown in the Languedoc-Roussillon region of France where it was known as Morrastel (which can be confusing, as Morrastel is a Spanish synonym for Mourvedre) but it was uprooted in the late 20th century in favor of hardier, more productive varietals, especially something called Morrastel Bouchet which was a crossing between Graciano and Petit Bouschet developed by Henri Bouschet . There is some grown in Australia, where it is known as Morrastel (though some of this may be Mourvedre as well), and some grown in California, where it is known as Xeres. It is thought that Portugal's Tinta Miúda may actually be Graciano.
One might be inclined to think that Graciano has been relegated to blending grape status because it is an inferior grape. In fact, Oz Clarke says that it is "far and away the most interesting red vine in Rioja," and Jancis Robinson writes "it is to the Riojanos' shame that so little Graciano survives in their vineyards today." If the wine is so good, then why, as recently as 1999, was vineyard acreage so low that the Spanish government was giving subsidies for planting Graciano in Rioja vineyards? The answer is that Graciano is notoriously low-yielding and susceptible to downy mildew, which means it needs more attention in the vineyards. It's an economic decision that it's hard to find fault with on a large scale. If two vines take up the same amount of space in the vineyard but one produces considerably more fruit and doesn't require as much maintenance, then why would you bother with the one you have to spend more money maintaining and get fewer bottles of wine from?
Fortunately, the fine wine boom of the past twenty years has encouraged more producers to devote more time and resources to cultivating Graciano. Many producers are letting Graciano be the sole star of their wines, producing 100% varietal Graciano wines. I was able to pick up a bottle produced by Vinos Sin-Ley, which is an interesting organization that you can read more about here. The bottle I picked up was the 2008 Traza Gra 2 which I got at Vino Divino in Brookline for about $16. In the glass, the wine was inky black almost all the way out to the rim with very intense saturation. The nose was a little reserved with black fruit flavors like blackberry preserves, black plums and blackcurrant. On the palate, the wine was medium/full bodied with high acid and plush tannins. There were flavors of dark chocolate, espresso, smoke, charcoal, blackberries, blackcurrants and black cherries. This is a dense, intensely packed wine full of dark fruits and earthy flavors that is nicely balanced by the high acid content. This was a little tight right now and could probably stand a little more time in the bottle, but Graciano is generally known as a wine that does not benefit from extended bottle age so a year or two tops should help unwind this a bit.