Website/Catalog  (1935)  Page(s) 19.  
 
May-Flowering Pæonies.
Herbaceous species and varieties.
Arietina. Purple Emperor. Single, bright rose, large, with golden stamens. Fine....3/6

Book  (1907)  Page(s) 78.  
 
800. EMPEROR, PURPLE; P. arietina.
(1) 1893, The Gardening World. Vol. 9, p. 642.
(2) 1899, Peter Barr & Son. Cat.
(3) 1900, Cyc. Am. Hort. p. 1191.
(4) Cornell Plot No. 548.

Magazine  (10 Jun 1893)  Page(s) 642.  
 
Single Pæonies.
These are now mostly out of bloom, but in spite of the dry weather, they made a fine display during last month, and might have been seen at their best as early as the first week in May, in the nursery of Messrs. Barr & Son, Long Ditton, Surrey. [...]
There are several distinct varieties of P. arietina, differing chiefly in the size and colour of the flowers. P. arietina Purple Emperor has rich dark purple flowers; and in the case of P. arietina Diogenes, they are of a rich rose red.