Well, unless it miraculously develops a deep pink/purple coloring in the next twenty minutes, its not 'William III'! Neither is it 'Stanwell'. The only three Spinosissimas I have firsthand knowledge of are those two, and 'Suzanne', and it's none of those.

It's not what I am growing as 'Mary, Queen of Scots'. I think there are several different roses going around under that name. Mine came from Sequoia and is a purple marble.

Also agree it is not Stanwell Perpetual or William III.

I also grow 'Mary Queen of Scots' (ex Vintage, but they seem to have been confused about what they actually had, too, reading their last catalog...in any case, mine looks the photos of MQoS on HMF under that listing...). Yours doesn't look like it.

Photos from this morning:

This was labeled Mary Queen of Scots at the Brooklyn Botanic Garden last week. There seem to be several roses going around under this name. But none are white or blush like the one in the OP.

@Ellen Harold Your photo of the Brooklyn Botanic Garden rose looks like what Vintage said, in their final catalog, was the actual name of what they were selling as 'Mary Queen of Scots': 'Glory of Edzell'. Of course, what Vintage sold/sent to me as 'Mary Queen of Scots' looks nothing like 'Glory of Edzell' -- see photo above! Confusion, confusion, confusion...

What strikes me is the tiny size (3/4" diameter) of the mystery rose bloom -- seems like that may be distinctive.

The same cerise-colored plant from Brooklyn is pictured on Helpmefind, along with several others of varying colors also identified as 'Mary Queen of Scots.'

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The white rose of the OP, on the other hand, looks like what one reads about in literature as the Scots rose of Anne of Green Gables, which Anne plants on Matthew's grave in the story. Of course if the flower stays cupped it would look smaller than a fully opened single flower. http://www.peterboyd.com/rosapimp14.htm

I also have a recent RVR's William III that is almost blooming for the first time. I'll post photos of what I got when it blooms.

I also had a William III I got from Vintage years ago and left in Alaska. That was the real thing.

I also have a William III from Greenmantle that may not bloom this Spring.

I also have Dominie Sampson (RVR), Suzanne, Falkland, Alberta Bouquet, William IV, Beauty of Leafland, Dooronbos Selection and Mrs. Colville.

When my new William III blooms I'll post what I got.

Many thanks to all who have commented so far. At least it seems we know what it's *not*! And it seems there's just a lot of confusion about these early-19th-century spinosissimas, in general.

The first bloom on my plant is now fully open -- it is no longer as cupped, and is just over 1" across. Palest blush color.

Sheila, it sounds like you might have the key to this puzzle. I'd be particularly interested to see your 'Dominie Sampson', as that is the one spinosissima (of RVR's four) that mine seems to most closely resemble...

These roses have a poetry about them that is unique.

That looks great, Ross. I'll have photos soon. Very late Spring here.

I would like to think that's the real Mary Queen of Scots, pace Brooklyn Botanic Garden. It's distinctive and with a touch of melancholy. Her tragic namesake is buried in Westminster Abbey next to her cousin, Queen Elizabeth, who had her imprisoned for years and then executed.

A few years ago we saw the opera Maria Stuarda with Sondra Radvanovsky -- her voice soaring over the orchestra -- fortissimo. It was unforgettable.

On the video it is brief but during the performance it seemed to float on and on -- to where we were, high up in the inexpensive seats in the Family Circle (opera singers are never miked).

https://youtu.be/BeO4YJrNUC8?t=30

https://www.classicroses.co.uk/roses/mary-queen-of-scots-shrub-rose.html

So I finally got the old pictures from my old computer.

Mary, Queen of Scots

And this was the best I could do.

William III (from Pickering)

Cultivars in general are a fairly recent innovation. So many Scots roses are called things like Double Blush Burnet, which is a name that could easily get applied to several different cultivars.

The rose Mary McMurty drew as 'Mary, Queen of Scots' looks nothing like anything I've seen with that name on this side of the pond. It is darker, more double, and notable for a silvery reverse.

Mary QoS from Trevor White in the UK(which I have on my allotment) is very similar in colouring to your rose, Catspa, but has more petals. Semi-double, bright lilac pink with paler edges, slightly marbled with paler reverse

Here is my William III from RVRs.

William above

Mary Queen of Scots from Vintage above

Beauty of Leafland from Leonard Heller.

Dominie Sampson and Falkland have not bloomed yet.

Prairie Peace just starting.

Above are Dominie Sampson from last year, and the red is Dooronbos Selection.

Falkland from Leonard Heller from last year. Hopefully, I'll get a better photo this year.

Sigh. Each one prettier than the other.