Magazine  (Sep 1977)  Page(s) 22.  
 
"Botanical Descriptions of 40 Saunders Lutea Hybrids" by Dr. David Reath and Silvia Saunders
...These descriptions aim to provide the nurseryman and the average gardener with a means of determining the differences between the hybrids, many of which are very similar indeed...
Thunderbolt—Very single; 10-13 petals, deep crimson, with black or scarlet streaks but no flares. Streaks on outer petals as well. Flares none. Filaments dull red. Stigmas (about 5) tall, crimson. Sheath blackish-purple. (Stigmas darker, filaments lighter, than in Black Pirate.) Foliage rather finely-cut. The plant may have laterals.

Article (magazine)  (Jan 1955)  Page(s) 25.  
 
Varieties Raised in America. All by Professor Saunders...
The "Black Pirate Group." Crimson to very dark, almost black maroon, single to double...
'Thunderbolt,' (1948)

Book  (1944)  Page(s) 104.  
 
For next year 1945
Make a master list of tree peonies to be grafted & check them off as done.

...13014 7 [grafts]

Book  Page(s) 9.  
 
13014 1940 Very bear B. Pirate. Shown in Boston 1940
1940 8 grafts in 10(2) 1941 Scarlet underlay...

Book  Page(s) 31.  
 
Thunderbolt 13014