There must be a difference between the plants called 'P. decora Anderson' in the pre-sternian classifications and the 'Decora Alba' used by A.P.Saunders during this time for his hybridizations. My opinion: It must be P. hellenica or P. clusii
Peonies, The Manual of the American Peony Society, edited by James Boyd © 1928 American Peony Society:
P. decora. "The alliance of this is to P. arietina."—Baker. Native to Anatolia, Serbia, etc. Flowers crimson.
Varieties:
alba
Ianthe
elatior
Pallasi
Gertrude Jekyll
Decora of Monte Gear
