The Tettnang is one of Germany's most famous hop-growing regions, and the landrace there is properly called Tettnanger. Tettnang hops from the Tettnanger are therefore known as Tettnang Tettnanger. True Tettnang Tettnanger hops are one of the universally recognized noble hops; they are closely related to (if not indistinguishable from the Czech Saazer cultivar and are greatly prized in brewing traditional German lagers and Wheat beers.
Noble hops are never considered to have the same character when grown outside of their native terroir; however, "Tettnanger" hops have still been grown in several other countries. However, recent analyses have revealed that in fact almost none of these so-called "Tettnanger" hops actually represent the same cultivar as the German landrace, but are in fact Fuggle or a cultivar closely related to Fuggle.
The most likely explanation is that the American and Australian "Tettnangers" were exported as rootstock from Switzerland, where Swiss "Tettnanger" hops were traditionally grown; it now appears that these hops may have been Fuggle hops all along as well.