Roses have 100s if not thousands of varieties. Whereas flowers like hibiscus and oleanders have maybe 10s of varieties or less.
I understand that humans have actively played a part in artificial selection of roses but is that the only cause ? Are some flowers just more “prone” to mutations than others ?
Some of this probably has to do with what we humans choose to consider as a different ‘variety’ of a plant. Like in roses, each different color is often considered a different variety. In other species, they come in a variety of colors, but are all considered the same variety.
Lots of varieties of some vegetables too. This thread discusses the several varieties of cabbage, all of which are one species, to the surprise of several posters there.
Elsewhere in that thread, someone mentions the many cultivars (breeds) of dogs.
Issues:
Desirability. Roses are an incredibly popular flower. So a lot of people, pros and amateurs, spend time coming up with new varieties. Not so much interest in phlox so fewer varieties.
Gene pool. Some types have several wild varieties which provide a larger gene pool to go exploring in. Others not so much. In addition, some species have a more robust genome and others hardly any variation.
Compare to dogs and cats. Dogs have a wide set of genes floating around. So you get an incredible range of sizes and shapes. Domestic cats come from a very small stock so not nearly as much variety. (A lot of felines have this trait.)
Roses have been hybridized from many species from all over the world, since the 18th century. The genus Rosa is a vast one. By the early 19th century “doubling” or the mutation which increases the number of petals (all species roses have a simpe rim of petals) had been developed in European/Middle Eastern hybrids that the petals were packed so tightly some roses could barely even open. These were the Damask (from Damascus) hybrids from which attar of roses is still collected. The main reason roses were originally cultivated was for their scent.
The biggest leap in popularity came with the introduction of Chinese species (the Tea Roses) which were repeat bloomers – previously all garden roses bloomed once a year. Combining qualities of the European hybrids and the Teas gave us Hybrid Teas, which completely dominate the market now along with the low shrubby floribundas which are also from Asia. Because of the vast range of genetics, roses come in a wide array of colors, and sizes from miniature pot roses to gigantic climbers which can cover a building.
In vegetables, there are actually far fewer varieties than there once were. In the past several decades there has been a lot more interest in reviving these ‘heirloom’ varieties. At one time for example, carrots came in every possible shape and size and color (white, purple, black, orange, red), but by the 1960’s there were only maybe ten, eight of which were only carried by seed companies catering to home gardeners. I am seeing those multicolored carrots again in farmers markets and local food co ops now. Agribusiness has attenuated all varieties of fruits, vegetables, and grains, down to a few dozen where there were once thousands. It is a great loss to genetic diversity.
I have a apple guy who comes and helps me with my remaining century old apple trees. He is one of the orchardists who collect scion wood from the many hundreds of named and un-named apple varieties being lost to us as these old trees die. In a supermarket you might get five or six kinds, and they will all be those which can be grown in Washington state under industrial conditions. It’s the same with everything from chickens to petunias. Like everything in the modern world, there is an illusion of unlimited choices but in reality, it’s three choices that have already been made for you, all made by the same company.
As Ulfreida notes, there are numerous classes of roses with particular climatic niches and habits, as well as crosses between those classes, so there’s a huge amount of variation and named cultivars.
Roses have had medicinal and even edible uses* in addition to be grown for beauty and scent. Since many if not most are “hardy”, surviving considerable frost, they’ve spread around the world much further than ornamental hibiscus and oleander.
*there are edible applications for certain hibiscus, not so for oleander. That is, unless you take into account dingbats who promote “oleander tea” as a remedy for cancer. Do not try this at home.
You can get patents on unique plant cultivars. In some cases, that can be quite profitable.
The patents are mixed in with the usual stuff at USPTO. Might be different in other countries.