Different species of a single genus can avoid cross-breeding by a variety of mechanisms. One of these is for the flowers to be receptive at different times of the day, even when they bloom during the same season. And “time of day” usually translates to “preferred temperature”.
For example, Gladiolus tristis is a South African species is normally pollinated by night-flying moths. Takatsu et al. (2001) found that the pollen tubes of this species grow fastest at 20°C [68°F], and fertilized the flowers most effectively [best fruit-set] at 15°C [59°F]. To the contrary, the garden variety ‘Traveller’ favored 30°C [86°F].
The difference in time-of-day receptivity also applies to roses, and is sometimes indicated by the release of perfume at only when needed to attract pollinators (not us, by the way). For example, Fernald (1926) found that Rosa nitida becomes fragrant in the dark. So does Gladiolus tristis. I don’t know what Nitida’s preferred temperature for pollination is, but I’m guessing that “cool” would be close.
Heslop-Harrison (1921) wrote, “I therefore got up earlier, at 4 a.m. (GMT), before any insects were at work, when I found that even then every newly expanded R. pimpinellifolia had its stigmas powdered with pollen from its own overarching stamens.”
Then, W. Paul (1848) quoted Boitard: “… M. Noisette, a French cultivator, has never sown seeds of the Chinese Roses (R. INDICA) without raising some Scotch Roses (R. SPINOSISSIMA) from them. He states, This fact is not supported by a solitary occurrence, but has been frequently observed by that cultivator, and is further attested by the evidence of M. Laffay, who raises seedlings on an extensive scale, and has this year between 200,000 and 300,000.”
Similarly, Thomas Rivers (1843) described his own observation:
“About four years since, in a pan of seedling Moss Roses, was one with a most peculiar habit, even when very young; this has since proved a hybrid rose, partaking much more of the Scotch Rose than of any other, and till the plant arrived at full growth I thought it a Scotch Rose, the seed of which had by accident been mixed with that of the Moss Rose, although I had taken extreme care: to my surprise it has since proved a perfect hybrid, having the sepals and the fruit of the Provence Rose, with the spiny and dwarf habit of the Scotch Rose; it bears abundance of hips, which are all abortive. The difference in the fruit of the Moss and Provence Roses and that of the Scotch is very remarkable, and this it was which drew my particular attention to the plant in question; it was raised from the same seed, and in the same seed-pan, as the Single Crimson Moss Rose: as this strange hybrid came from a Moss Rose accidentally fertilised, we may expect that art will do much more for us.”
The Scotch-Moss rose, ‘Andrewsii’ must be of similar origin.
I won’t get into the Spinosissima/Pimpinellifolia mess. It is apparent that it/they can pollinate its/their own flowers, and have enough left over to fertilize other species that are receptive early in the morning … even if not quite so early as the pollinators. Heslop-Harrison also mentioned some hybrids of Caninae species pollinated by Pimpinellifolia.
It is also apparent that the Indica group and the Provincialis group are receptive at about the same time. Thus, the Bourbon roe.
The next clearly marked group are species that are fragrant in the evening or dusk.
Allen: Rosa arvensis: A problem wild rose (1987)
“After the circulation of my information paper in 1979, John Watts, in North Wales, made some careful observations in the Conwy area, where the species is common locally, and he reported the flowers as scentless by day but sometimes having a faint scent, just discernible, at dusk in warm weather.”
HelpMeFind: Rosa clinophylla (5 Mar 2022)
Plazbo (Australia): “Not quite night night yet but just past sunset (but can still mostly see without a torch if that makes sense) and it’s very mild and inoffensive. The flowers close up at night though so nocturnal pollinators would be ‘locked out’ as it were.”
This may explain why it has been so difficult to repeat the cross that produced _R. _x hardii. The Hulthemia pollen must last long enough to pollinate the R. clinophylla blossoms around dusk, and still find the temperature suitable.\
Rosa moschata (the only specimen I have had many opportunities to sniff) is fragrant in the morning and afternoon. But a close cousin (?) is different.
Sprenger: Rosa moschata var Korfuana (1923)
“They smell particularly fine in the late evening, at night and in the fresh morning. During the day their volatile oil seems to evaporate so rapidly that little or nothing remains perceptible to the human sense of smell. It is a mild, pleasant musky scent. One collects the rosettes for its sake, to put them between the laundry and clothes, but also in winter to stretch the tea with them, which then regulates the digestion better.”
For links and more examples:
http://bulbnrose.x10.mx/KKing/TemperatureFertility.html
