We have grown D. lutea for a long time from seed collected in the Picos de Europa. One plant rather surprisingly won a Certificate of Merit at Leeds AGS show some years ago, surprising not only because of the debate as to it's actual identity at the time, but also since it was one of those 'Oo, that looks nice let's dig it up' last minute entries!
We resolved the issue by reference to a substantial tome published by the Basque government entitled 'Claves ilustradas de la Flora del País Vasco y territorios limítrofes', a book no longer available in print but which can be downloaded free on the net from Jolube. Well worth a try - even if you have to use online translation for the details!
The other Spanish species we grow, also from seed from the Picos de Europa, is D. Parviflora.
The pics were taken this morning and show both plants pretty much at their best.
The last pic is an old one of D. grandiflora which grows for us in deep shade.
JohnnyD