Blaufränkish or Blauburgunder). Of course, that may immediately lead to another question: why does a grape called "Portugieser" need a Germanic prefix? Well, Austria and Germany are the most prolific growers of Portugieser, as it is the third most planted red variety in each of those two countries (it occupies between 4,000 and 5,000 hectares in each). The vine is also widely spread throughout Eastern Europe and is grown in Croatia, the Czech Republic, Romania, Slovenia, and Hungary, where it is one of the permitted grapes in the Bull's Blood blend. It was even once widely grown in southwestern France, where it was known as Oporto or Portugais Bleu. So where does it rank in Portuguese production? Well, it doesn't.
As far as I can tell, Portugieser isn't actually grown in Portugal at all. In fact, depending on what sources you use, Portugieser may not have any connection to Portugal whatsoever. The Austrian Wine website maintains that the grape is native to Portugal and was taken to Austria by the Baron von Fries in 1770. Most other sources, though, indicate that the grape is native to Austria with no apparent or proven link either to Portugal or to any other Portuguese grape. The von Fries origin story must be persistent, though, as most of the synonyms for Portugieser incorporate some reference to Portugal: Kékoporto in Hungary, Modrý Portugal in the Czech Republic, Portugaljka in Croatia, etc. (those who are terribly interested can peruse the full list of synonyms here). I suppose it's possible that wines made from the Portugieser grape reminded the drinkers of wines from Portugal, but that seems unlikely given the grape's reputation for producing pale, light bodied red wines, a far cry from the powerhouse Ports that were likely in circulation in the 18th and 19th Centuries.
Whatever the true origin of the name is, the grape is now widely known as Portugieser and is relatively widely planted, though little of it gets exported. Mostly this is because the wines made from the grape have a pretty lousy reputation. The Oxford Companion to Wine writes that Portugieser is a "black grape variety common in both senses of that word in Austria and Germany" which "can taste disconcertingly inconsequential to non-natives." They further write "such wines are rarely exported, with good reason, and are only rarely worthy of detailed study." So why does the grape take up so much real estate in these countries?
Well, the main reason is that Blauer Portugieser is really easy to grow. It is resistant to a wide range of vine diseases, most specifically coulure, or poor fruit set (when the berries are very young, many of them fall off, which is called coulure). Because of its resistance to this particular affliction, Portugieser is an explosive yielder, sometimes producing as much as 120 hl/ha of juice, or around 7 tons of fruit per acre. As you might expect, if the vine is allowed to produce to its full potential, the resulting wines are dilute and the grape's naturally low acidity is stretched even thinner. There are some producers who are trying to produce fine wines from this unappreciated grape by restricting yields, using old vines and barrel-maturing their wine.