Let's get some history out of the way first: some sources say that Lagrein was first mentioned in print in the 17th Century, but other sources claim that mentions of the grape can be dated as far back as 1379 AD. For awhile, it was thought that the grape came over from Greece and that the source of the name "Lagrein" was either from the Greek word lagarinthos, which means "hanging," or from the Greek Colony of Lagaria in southern Italy. Today, most people seem to think that the name comes from the Lagarina Valley in Trentino, just south of Alto Adige. Whatever the source of the grape's name, its origin is no longer in doubt: genetic testing has shown that one of its parent grapes is Teroldego and it is a full sibling of Marzemino, both native Trentino varietals (Vouillamoz, J., & Grando, M. (2006) Genealogy of wine grape cultivars: ‘Pinot’ is related to ‘Syrah’. Heredity, 97(2), 102-110.). (**UPDATE** Lagrein's parentage has been confirmed as Teroldego x Schiava Gentile according to: Cipriani, G. et al. The SSR-based molecular profile of 1005 grapevine (Vitis vinifera L.) accessions uncovers new synonymy and parentages, and reveals a large admixture amongst varieties of different geographic origin. 2010. Theoretical and Applied Genetics. 121: 1569-1585.). These relations strongly indicate that the grape was born in the Trentino/Alto-Adige region. Today, it is extraordinarily difficult, but not impossible, to find Lagrein anywhere outside of Alto Adige. Australia seems to be the only other place on earth bothering with the grape, though production there is limited to a handful of producers (California has some vines, but nowhere near enough to be considered a player in the Lagrein game).
The vine was once more widespread through Alto Adige than it is today, but it was supplanted by Schiava to a large extent. Both Schiava and Lagrein are capable of very high yields, and while I've read that Schiava was supplanting Lagrein because of its greater resistance to disease, my feeling is that fashion probably played a larger role. The focus on denser, darker red wines is largely a product of recent history as, traditionally, most red wines were fairly light in body and color (many historians think that the great "clarets" from Bordeaux in the 17th and 18th centuries were closer to modern day rosé wines than red wines). In general, Lagrein is not a light wine and it has the double-whammy of high acidity and very high tannins. My feeling is that Schiava was more widely planted because the wines produced from the grape were more approachable and user-friendly than the wines being made from Lagrein. A good deal of the Lagrein production was used to beef up the Schiava a bit, as Schiava can be bewilderingly light in color for a red wine. It's also somewhat telling that, for quite awhile, Lagrein was more lauded for its ability to produce an excellent rosé than for its ability to produce red wine (it still has a great reputation for rosé production, though it is much more difficult to find rosé wines made from it than regular red wines).
Current fashion has swung in the opposite direction and today's consumer is more interested in denser, heavier red wines with more body and fruit. While Lagrein does have high acid and high tannin, it also has the great equalizer of intense fruit concentration that can round out the sharpness and provide a lot of flesh on the otherwise pretty angular skeleton that the Lagrein grape carries around. The key, though, is a focus on quality in the vineyard. As mentioned above, Lagrein has the capacity to yield explosively but when allowed to do so, the fruit gets diluted and the structure sticks out in all the wrong places. Canopy management and restricted yields are especially key for producers who are looking to produce quality wines from Lagrein. Many producers are heeding the call, though, and Lagrein is starting to take back some of the vineyard area from Schiava and to generate more of a buzz in the international community.
Sel de la Terre was offering the 2003 vintage of the Abtei Muri-Gries Riserva for $40 a bottle when I was there in April 2011 (the picture on the side shows the 2000 vintage because I wasn't able to snap a picture in the restaurant and this was the best looking label I could find). I jotted my notes down on some scrap paper so this isn't a complete tasting note, but the bottle was so good I definitely wanted to be able to write about it here. The lighting in the restaurant was pretty dim, but the color on this wine was an obvious, dense, inky purple color. The nose was pretty shy on this and never developed very much. On the palate, though, the wine was full, dense and richly extracted with acidity on the higher side of medium and grainy tannins. The palate was full of rich, ripe purple fruits and nice earthy, leathery notes. It was broad and very well balanced with a medium finish. This wine is produced in a monastery in Alto-Adige from three different estate vineyards that only total 9 hectares. Some of the vines on these estates are 80+ years old. The wine is stainless-steel vinified and then aged in wooden barrels (probably some new oak, but I doubt it's 100%) for 16 months prior to release.