The common tall double one gets called D. scabra 'Plena'. You may have to do some serious research to determine if that name truly applies to this particular specimen. The height is not remarkable, there are more kinds of them taller than D. gracilis, D. kalmiiflora and of course the ~creeping 'Nikko' than there are of the shorter ones. As with other groups smaller types have become more prominent as gardens have shrunk.
