Article (website)  (16 Jan 2019)  
 
The name ‘Mary Queen of Scots’ is applied, in commerce, to at least two very different cultivars of Rosa pimpinellifolia. One of these is a plant with very distinct double purple flowers with pale backs to the petals (‘Bicolor’ in the 1820s sense) and rounded black heps; another as a plant with single pale pink flowers irregularly marked with darker pink which develop into elongated dark red pendulous heps (possibly one of a number of hybrids between R. pimpinellifolia and R. pendulina). It is very unlikely that either rose has any association whatsoever with the 16th century woman of that name. 

Newsletter  (Sep 2018)  Page(s) 15. No. 18.  Includes photo(s).
 
[From "Scots Roses And Related Cultivars Of Rosa Spinosissima", by Peter A. Boyd, pp. 8-17]
However, Peter Beales applied the name ‘Mary Queen of Scots’ to a completely different rose (Beales, 1997). His rose is not a typical Scots Rose in character. It is clearly a form of R. x reversa (R. spinosissima x R. pendulina). It has single pink flowers with darker pink markings and elongated dark red heps. The example is even more complicated by the fact that the name ‘Mary Queen of Scots’ is not one of the hundreds of cultivar names that the present author has found used before 1962 and the rose described by Thomas is probably ‘Bicolor’, as illustrated by Andrews (1822) 

Article (magazine)  (2008)  Includes photo(s).
 
Mary Queen of Scots. The rose described by Graham Thomas (1962) is a typical Scots Rose with distinctive white or grey buds opening to semi-double purple flowers with white backs to the petals. It tends to flower later in June than the other Scots Roses. It is similar to the rose called 'Bicolor' in the early 19th century and I have not found the name 'Mary Queen of Scots' used before the 20th century. This rose is sometimes sold under the name 'Queen Mary' by nurseries in Europe. This semi-double rose is quite different from the single rose described by Peter Beales (1997). See 'Mary Queen of Scots' below (under R. x reversa 'group'). 

'Mary Queen of Scots'
This name was used by Peter Beales (1997) for what seems to be a cultivar of R. x reversa with single pink flowers with irregular, darker pink shading and elongated, deep red fruits. This is quite different from the semi-double purple Scots Rose with this name described by Thomas (1962) which I discuss above. The single-flowered plant is what is normally sold by nurseries under the name 'Mary Queen of Scots', but the Thomas use of the name has priority. Ideally, the name of the single flowered cultivar should be changed. It flowers early, at the same time as 'Glory of Edzell'.

Website/Catalog  (1983)  Page(s) 28.  
 
Mary Queen of Scots.  (spinosissima) A beautiful little rose. Single flowers of off-white to cream with lilac undertones and reddish markings around the edges of each petal. Pronounced anthers. Blackish-maroon fruit. An old variety.  Shade tolerant.  H. G. W. F. 4 x 3’.