A Quick Look at the Rose Subgenera

Roses are native to locales all across the Northern Hemisphere, and there's a lot of genetic diversity within the genus (little of which is found in the mainstream cultivars, however). Taxonomists have placed the vast majority of rose species within subgenus Rosa, which is further divided into many sections. These are the species one typically thinks about when roses are considered.

Rosa glutinosa, in subgenus Rosa, section Caninae. Like R. eglanteria (also in Caninae), this species has glandular leaves and buds which exude pine-to-green-apple-scented oils.

Rosa carolina, type of section Carolinae within subgenus Rosa. Although the flowers are typically medium pink, this one was bleached to white in the sun (a tinge of pink still remains).

Next we get into the relatively weird subgenera, which could be considered to be on the genetic fringes of the genus: Hulthemia, Hesperhodos, and Platyrhodon. Their separate status is confirmed by their general unwillingness to breed readily with members of other sections, as well as very distinct morphological characteristics.

Rosa persica, the sole member of subgenus Hulthemia, was once placed in its own genus under the moniker Hulthemia persica. It is native to the Middle East, where it grows as suckering briar. The species itself is notoriously difficult to cultivate, and the close hybrids are also known to be finicky.

This one is really fascinating-- it's sort of a rose, but there are remarkable differences, especially the simple rather than compound leaves. (Photo credit)

Breeders have been working to incorporate the red eye into mainstream garden cultivars-- notably James Sproul (here's his excellent blog). Even in F1 hybrids, the offspring retain the compound leaves of the other subgenera, and so far the red eye has been the only hulthemia-derived characteristic of note.

Hesperhodos carries on the desert briar theme somewhat, as the two Hesperhodos species-- R. stellata and R. minutifolia-- are native to southern California and Mexico. These species have been given almost no breeding attention-- but you can read about some of Kim Rupert's exciting developments with Hesperhodos here and here. R. stellata mirifica is considered to be the most approachable form-- Graham Stuart Thomas reported that it grew well in Surrey; it's currently available from Greenmantle Nursery. Unfortunately I don't think there is a commercial source for minutifolia for US gardeners.

R. stellata (Photo credit)

This slightly sunburnt R. minutifolia barely looks like a rose! The leaves remind me of angel pelargoniums. (Photo credit)

Last is Platyrhodon, perhaps the easiest of these fringe roses to grow. It has long been included in US gardens and is commonly known as "the chestnut rose" for its nutty-looking hips. The most frequently seen form, R. roxburghii, is actually the double variant (given this name since it was the first to be documented by Western botanical explorers). The actual vanilla species, with single flowers, is known as R. roxburghii normalis. These can grow to be very large shrubs, having thick stems with brown, peeling bark.

R. roxburghii (Photo credit)

R. roxburghii hips

Detail of a particularly woody roxburghii stem (Photo credit)

While these species are very interesting in their own right, it is particularly mind boggling to consider that these plants are in the very same genus as the hybrid teas! Perhaps the diversity of Rosa is a large reason why it has so many devoted experts. Since amateur hybridizing seems to be very involved with the species at the moment, I think that as time progresses we will have more access to plants with these "fringe" genetics.