I still remember the first time, now over a half-century ago, I saw a moss rose: my high school biology teacher, Miss Boyer, had brought one from her garden to class. I remember spending some time examining it carefully, enjoying the fragrance of the flower and the resinous fragrance of the branched glands which give this rose its name. This fragrant resin clings to whatever touches it, and if you stroke the soft moss or draw the mossy stem across your lip, you will be able to take the fragrance with you and enjoy it for hours.
The bud shown in the image above is that of the so-called common moss rose, although it’s anything but common in either the literal or figurative senses. Surely someone in my gardening circle must grow moss roses, but if they do, I’ve never seen them. And among roses, the moss roses are anything but common.
The moss mutation seems to have occurred several times in roses. Graham Stuart Thomas made a firm distinction between the soft moss of the moss roses derived (probably by somatic mutation) from the cabbage rose Rosa 'Centifolia' and the hard moss which characterizes the moss roses derived from the autumn damask rose. In addition to these, there are numerous hybrids in which the moss effect is found; these mostly have moss roses of the autumn damask sort in their background. I’m not aware of any hybrid moss roses which can be said with certainty to have the common moss in their background. However, it is said that a single-flowered (i.e. with few petals, viable pollen and capable of setting viable seed) mutation occurred in the early nineteenth century, and from this plant many hybridized mosses were raised.
With all of that in mind, it's evident that there are several sorts of roses which are being called moss roses. Four groups make sense to me: 1) the mosses derived as somatic mutations from Rosa 'Centifolia' 2) the mosses derived as somatic mutations from Rosa 'Bifera' or, as it is often called 'Damascena Bifera'; 3) the hybrids derived from the single-flowered mutation of the common moss rose; and 4) the hybrids derived from the mossy mutation of Rosa 'Bifera' aka 'Damascena bifera'.
If it is true that the common moss originated as a bud sport of the cabbage rose Rosa 'Centifolia', then it can be said that the moss rose and the cabbage rose are pieces of one original seedling; in other words they form a variable clone. And if the single-flowered mutation mentioned above was in fact a bud sport, then it, too, is a part of this same variable clone.
A word seems necessary about the formatting of the names. In old books it's usual to see the names Rosa centifolia and Rosa damascena bifera, the names italicized as if the plants in question were species. These are in fact ancient hybrids. The one known as 'Centifolia' (the name here formatted to reflect the belief that it is a clone of garden origin) seems to have originated in the late seventeenth or even early eighteenth century; it is the "perfected form which produced the moss rose" (to use Dr. Hurst's phrase as quoted by Thomas), the ultimate form in a series of hybrid roses which had been in development for about two centuries among the Dutch. The Romans used the term "rosa centifolia" for a rose they knew, but it was not this plant.
Rosa 'Damascena Bifera' or Rosa 'Bifera' is said to be a hybrid of Rosa gallica and R. moschata. This plant is of truly ancient origin, and might have been known to the Romans of the Classical period.