According to the RHS Plant Finder 2010-2011, your plant is now named as Salvia x sylvestris 'Dear Anja'. Salvia x sylvestris is supposed to be a hybrid of S. nemorosa and S. pratensis, and S. x superba is supposed to be a hybrid of S. x sylvestris and S. amplexicaulis. But this whole area is extremely confusing, there are so many hybrids appearing each year, and the fact that the species are all variable just adds to the confusion!

Whatever it is, 'Dear Anja' is certainly stunning. I did hear that Piet Oudolf named it after his wife.

Robin.