I don't know if all low petal count roses partially close up at night but certainly most of them do. I don't have any singles now but I recall that they close up with the petals coming together and touching.

Yes, almost all single roses do that. I know of only two large flowered singles that do not -- Altissimo and Frankie, and one mini single -- Lavender Spoon. All of those have enough substance to stay open, once open.

And actually most breeders try to breed that trait out of their new creations -- the propensity to close again once open.

I've seen my Mrs. Oakley Fisher, Mutabilis and Lilac Charm do this. It's cute, I think, when they are a bit crumpled...but then I'm usually a bit crumpled too.
Susan

I know my Dainty Bess, golden Wings and Mutabilis all close at night. I like the trait myself. Makes them look rather shy.

I bought quite a few of these older HTs from Vintage too. They are just starting to bloom - they are really interesting - one has a big full bloom of rich pink with lots of petals, another is a deep Chinese red......so sad to think all these are going to no longer be in commerce. Maybe one day enough budwood will be passed around and some nurseries will start carrying them again. I have Golden Wings - it is really a pretty thing! I saw an older bush that was blooming its head off, so had to have it.