Article (magazine)  (2005)  Page(s) 453.  
 
R. x hollandica: In the British Isles and elsewhere, naturalized R. rugosa may be confused with a morphologically similar taxon of unclear origin and nomenclature. In continental Europe, it has most often been referred to the hybrid R. × kamtchatica Vent., which is said to have been introduced to France around 1770 (Bean 1980). However, recent authors hold that the introduced European plants are not identical to the native Far Eastern ones. Rutherford (1990) suggested that the name R. × hollandica should be used for this taxon, allegedly originating from a chance crossing in the Netherlands in 1888 between R. rugosa and an unknown species. Several species have been proposed as the other parental species. Most likely it is one of the diploid species R. majalis Herrm. or R. davurica Pall., which are closely related. The tetraploid R. palustris (Verrier 1991; in which case the name would be R. × spaethiana ‘Hollandica’) and the cultivar R. × noisettiana ‘Manettii’ (Mang 1985) have been suggested as well. The flower flavonoid pattern supports the ancestry of one of the diploid species R. multiflora Thunb., R. davurica or R. wichuraiana Crépin (Mikanagi et al. 1994). Possibly, hybrids between R. rugosa and more than one species have escaped from cultivation and are now recorded under the name R. × hollandica.

Book  (11 Jun 1993)  Page(s) 27.  
 
R. rugosa x 'Manetti'. Spek (The Netherlands) 1888. Description. Frequently used as an understock (particularly for rose standards), but rarely grown deliberately as a garden subject... hardy.

Book  (Apr 1993)  Page(s) 248.  
 
Hollandica Hybrid Rugosa, Thought to have been raised by J. Spek, ca. 1888; Selected Dutch clone of R. rugosa, or perhaps a hybrid with Manettii, widely used as an understock, especially for tree roses.

Book  (1986)  Page(s) 179.  
 
Understocks...Hybrids...'Hollandica' (R. rugosa 'Hollandica'; R. 'Boskoopse Rugosa'; R. 'Scherpe Boskoop')

Book  (1981)  Page(s) 270.  
 
'Hollandica' (J. Spek, Boskoop, Holland, about 1888). Better known under its name 'Boskoop Rugosa', actually called Scherpe Boskoop', widely used as stock for budding; shrub rather high, branched, stems densely covered with prickles and bristles, these yellowish and unequal; leaflets large, bright green; flowers 5-10 together, single, dark red; fruits pendulous, globose, dark red, glandular. Much appreciated for stock use in wet ground, but suckers heavily.

Book  (1981)  Page(s) 113.  
 
R. rugosa hollandica (= R. rugosa x manettii; 'Boskoops's Rugosa') Various selected forms are to be found in Holland, e.g. 'Spek's Improved'. 
Very hardy, growth stiff and upright; gives large flowers in good quantity; widely used in Holland (and formerly in Germany) for standards, as it is only this variety that really thrives in the moist soil at Boskoop, where both canina and multiflora fail; a good stock for container roses.
Very prone to suckering; the budded plants are not long-lived; standards are not viable on this stock because they are very hard and easily broken; needs a light, sandy soil and a lot of moisture; only propagated by cuttings.

Book  (1978)  Page(s) 237.  
 
'Hollandica'....

Magazine  (1975)  Page(s) 81.  
 
Ook de R. multiflora 'Seven Sisters' voldeed niet, om redenen die niet worden genoemd. Het getij keerde echter toen A. Nijveldt in 1885 afwijkende vormen vond in Rosa rugosa zaailingen. Deze werden door J. Spek beproefd. Een van de zaailingen die opvieldoor sterke groei, kreeg zijn bijzondere aandacht en werddoor winterstek vermeerdend....

Translation:
The R. multiflora 'Seven Sisters' was also not suficient for reasons not mentioned. However, the tide turned when A. Nijveld discovered abnormal shapes in Rosa rugosa seedlings in 1885. These were tested by J. Spek. One of the seedlings that stood out for strong growth received special attention and was propagated by winter cuttings...

Newsletter  (1975)  Page(s) 759.  
 
Rosa rugosa grown for rootstock is probably a hybrid of R. rugosa x R. cinnamomea. Some selections out of this cross have been multiplied: the it common one is Spek's improved (BOOM, 1949).

Magazine  (1970)  Page(s) 33.  
 
Rose rootstocks ... R. 'Scherpe Boskoop'