Iris ensata  'Yezo Nishiki'
 
5th July 2014  
Recorded from 1896 in Tokyo. Introduced by Bertrand Farr in 1912. The name means Brocade of Yezo. Farrs catalogue of 1918 sys:
YEZO-NISHIKI. Very double variety; eight crimson-purple petals, heavily splashed white.
The description doesn't really fit my plant.
References:
The American Iris Society Encyclopedia, https://wiki.irises.org