Boissier Flora Orientalis 1:97 (1867)

From the book: Peonies of Greece William T. Stearn Peter H. Davis (1984):

.. named the Cretan peony (P. clusii) as P. peregrina var. glabra

and one from Mount Parnassus (P. parnassica) as var. latifolia and

recorded P. decora (i.e. P. peregrina) from “Rumelia”, the central Balkan region.

The truth of Boissier’s remark “species inter se valde affines difficile delimitandae” (the species closely akin to one another difficult to delimit) has been evident to every student of the genus from Linnaeus onwards.