There may be an obvious reason but I have never come across one in reading. Just from observation it seems that the closer that a seedling’s hereditary is to species, the more likely that the bloom will close at nite. I know that some plants have this same mechanism (blossoms closing when the light levels are equal to dusk or less) but it seems a bit more random with roses—except that species seem more likely to close. Is there a reason, or is this totally random? Would it follow that if this is true, it might be used as another clue to some species x modern crosses evidence?
I work with a lot of singles and semi-doubles and almost all seem to close to a certain degree at night. I’m thinking most roses would if they had fewer petals but we may not notice it in more heavily petaled roses.
American Rose Annual 48: 188-193 (1963)
A Self-Pollination Mechanism And Other Items In Rose Species
Dr. Eileen W. Erlanson Macfarlane
“In many wild roses the petals are past their prime by the third day and the flowers no longer close at night. The stamens may then rise up and their delicate filaments curve over to bring the pollen-bearing anthers onto the receptive stigmatic heads of the ovaries.”
http://bulbnrose.x10.mx/Roses/breeding/Erlanson/ErlansonColor.html
Good point about the singles. That is where I notice it most. I do have three red toned roses that do attempt to close at night and they are probably in the range of 20+ petals. This really knocks them out of the cut flower use. Otherwise very nice color and flower and shrub. I do not think it is related to petal ‘weight’ just because I see some pretty heavy singles closing. It does seem hereditary or is it more weather related?
In many other plants it’s about protecting sexual parts, the insects that pollinate them aren’t out at night, frost damage (due to temp drop at night), rain, etc.
It’s probably connected to that in some way.
I just happened on this note:
The American Gardener’s Magazine, Volume 1, p. 206 (June 1835)
Mr. Buist has a fine collection of Roses, among which are some of the most beautiful kinds; he also has raised several from seed, which are known by the names of R. Websterii, Jacksonii, purpurea, &c. The animated Daily is a very desirable rose, as it retains its form for many days, closing up every night, a peculiarity quite uncommon.
The description (below) of Buist’s ‘Animated’ seems to agree with the rose I saw labeled as ‘Bengale Animée’ at the SJ Heritage garden. I don’t know whether that variety closed at night because I never saw it at night.
American Flower-garden Directory: Containing Practical Directions … - Page 182 (1832)
Hibbert & Buist (Philadelphia, Pa.), Robert Buist
No. 2. *Rose Animated, daily, is a very fine rose, and its merits are appreciated by those who have it in their collections. It is more double, and better formed than No. 1 [Rosa indica, common China or daily], and partakes of the fragrance of No. 8 [Rosa odorata], is perfectly hardy, colour a fine blush, grows freely, and flowers abundantly; and is coming into great repute.
*Those marked thus * we have grown from seed.
Knight’s ‘Animating’ or ‘Animated’ was something altogether different.
Plazbo, those are such good points. And that excerpt from the American Gardener’s Mag., makes the point that this is a " peculiarity quite uncommon." It seems quite uncommon esp., among modern overly hybridized roses. We (amateur and professional hybridizers) may see this more often but particularly because we grow and work with so many species or close to species. What I was wondering is whether this was at least something of an indicator of hybridity when doing crosses so close to and including species, again especially when the hybridity of that cross may be in question?
I think the most important benefit of a flower closing at night is that it helps retain moisture for pollen germination.
Closing at night is something I have FREQUENTLY observed in semi single to single roses for the past thirty-plus years. Don’s suggestion that it may preserve moisture required for pollen generation may be the reason. I’ve always figured it also helped prevent the anthers and stigma from getting wet from nightly dews. Once they’e gotten soaked, they don’t appear to be as fertile as those which haven’t been soaked.