The External Structures of Leaves
by Rich Baer, Master Rosarian, Portland Rose Society
Having several degrees in the botanical field of study, I always approach any garden plant, including roses, as if they were just that, a plant. Botany is a very old science and as such has a language and terms to describe most of the various parts of plants and the descriptions pretty much cover all plants. So with that in mind, I would like to discuss some of those terms as they relate to roses so that when we talk we are all using the same language. It was sort of distressing to me that in talking to several American Rose Society Board members that they did not even know exactly what a leaf was. However they did know how to manipulate the petals so that they would be more likely to win a trophy at a show. Obviously knowing the parts of a leaf does not help in winning a trophy.
The picture below on the left shows a few typical rose leaves. Botanically they are defined as being pinnately compound. Pinnately compound means that the leaf has a major leaf stem, the Petiole, to which the leaflets are attached in a linear manner to the petiole with a Petiolule. The leaflets are attached opposite each other and there is one leaflet on the end of the petiole, so each leaf always has an odd number of leaflets. The number of leaflets in roses is usually unique to specific varieties. Most modern hybrid tea roses have leaves that are composed of five leaflets. However, as you reach the end of the flowering stem you will often find leaves that have three leaflets and then even closer to the bloom you may find leaves with only the terminal leaflet being present. The other type of compound leaf is called palmate where all the leaflets originate from a single point. (Chestnut and cannabis are examples.)
Above and to the left are typical leaflets of a rose. Most are ovate and have serrated edges.
If you look at the base of the leaf the petiole has a widened base. This structure is called the stipule. Stipules come in many widths and lengths although always occur before the first set of leaflets is attached.
A long time ago there was a little saying that you should not tell secrets in the cornfield because the corn has ears. Well, the same goes for telling secrets in the rose garden. Roses have ears as well. At the distil end of the stipule (the part furthest from the rose stem) are two small projections. These projections are known as auricles which translated into English is ears. The final picture is of a number of non-typical rose leaves that I found in the garden.
Many of the Old Garden Roses have many more than five leaflets, some of them have as many as 13 and maybe more leaflets. And among them are many different shapes of stipules as well, but the same structures are present in all rose leaves.
So there you have it, now you know almost everything there is to know about the external structures of rose leaves. The petiole is often referred to as the rachis. The rachis is often armed with prickles along its under side. Personally I am wounded more often by the prickles on the rachis than I am by the prickles anywhere (what we usually refer to as thorns) else on the rose bush. It seems, al least for me, I tend to forget that those prickles are awaiting me as I am doing my dead heading Baer handed.
All photos by Rich Baer