Book  (2019)  Page(s) 129.  Includes photo(s).
 
Natural Hybrids...Rosa x iwara Siebold ex Regel, Index Sem. Hort. Petrop. 1861:53 (1861), description

Newsletter  (Dec 2013)  Page(s) 33.  
 
[From "Seizo Suzuki’s collection of old roses and species roses", by Yuki Mikanagi]
In 1942, though Japan had already entered into World War II, Mr. Suzuki was continuing his field work, and found a natural hybrid between R. rugosa and R. multiflora (R. x iwara) near the estuary of the Toyohira River in Hokkaido, and a natural hybrid between R. rugosa and R. luciae (= R. wichurana) on the seashore in Ibaraki

Website/Catalog  (2006)  
 
Ko-Hamanasu (Small Shore Aubergine) syn. =Ko-Hamanashi (Small Shore Pear)
R. x iwara Siebold ex Regel
Index Sem. Hort. Petrop. 1861:53 (1861)
Estimated parentage: R. multiflora x R. rugosa

Article (magazine)  (2005)  Page(s) 452.  
 
In its native range [R. rugosa] hybridizes with R. davurica Pall. (syn. R. amblyotis C.A. Meyer) (Pimenov & Schroeter 1964 Ohwi 1965), with R. marretii Lév., which is its closest relative (Wu et al. 2000, 2001), with R. acicularis Lindl. (Charkewicz 1996), and with R. multiflora Thunb. (= R. × iwara Sieber ex Regel, syn. R. × yesoensis (Fr. & Sav.) Makino).

Book  (11 Jun 1993)  Page(s) 28.  
 
R. multiflora x R. rugosa. Japan before 1830. Description. Small white single flowers with separated petals giving the blossom a blackberry-like appearance... Its name means "rose thorn" in Japanese.

Book  (Apr 1993)  Page(s) 263.  
 
Miscellaneous Old Garden Rose, white, (R. x iwara Siebold ex Regel; R. yesoensis Makino); R. multiflora x R. rugosa; Cultivated prior to 1830. Description.

Book  (1965)  Page(s) 541.  
 
Rosa X iwara Sieb. R. yesoensis (Fr. & Sav.) Makino; R. iwara var. yesoensis Fr. & Sav. - Ko-hama-nasu. Natural hybrid of No. 5 [R. rugosa Thunb.] and No. 1 [R. multiflora Thunb.], differing from No. 5 in the less prominently rugose upper leaf-surfaces, and with smaller flowers 3-4 cm. across. Occurs rarely along seashores in Hokkaido and n. Honshu.

Book  (1936)  Page(s) 365.  
 
R. Iwara (hybrid rugosa) Siebold 1856; R. rugosa Th. X R. multifl. simpl.; white, 3 cm., medium size, double, cup form, clusters of 5-15, growth 7/10. climbing, 1.25m. Imported from Japan. Sangerhausen

Magazine  (Jul 1930)  Page(s) 91.  
 
Rugosa ibara. — Siebold, hybride de rugosa et de R. multiflore.

Magazine  (5 Aug 1911)  Page(s) 374.  
 
The Parentage of Roses.
The following list of the world's Roses and their parentage has been compiled by Mr. Robert Daniel, 38 Russell Road. Fishponds, Bristol, and by his kind permission we are enabled to publish it...
Rosa rugosa Yvara... Hybrid Rugosa, Siebold, R. rugosa X R. multiflora