Armed Rachis Can Leave You Bloody
by Rich Baer, Master Rosarian, Portland Rose Society
Thorns, prickles, spines what is the difference? They all hurt when you encounter them in the garden or elsewhere. They are different botanically because they all derive from different parts of the plant. Botanically roses do not have thorns, but are armed with what should be called prickles. However, calling rose prickles thorns goes back so far and is so familiar that there is not much likelihood that it will ever change in the minds of rose fanciers.
From Left to right: Prickles of Falling in Love Rose, Thorns growing on a Honey Locust Tree, Spines from a cactus plant
But botanically what is the difference? Let’s start with thorns. There are a number of plants that are blessed with thorns. Some common ones are the locust trees. Both Honey Locust and Black Locust have impressive thorns which may be quite large and branching. Another common thorn plant is the Hawthorn. What is it that makes a thorn a thorn botanically? Thorns are modified stems and grow much like stems because they originate from the nodes on the branches of the plant usually occurring from the axil of a leaf. They are not removable from the plant in most cases unless they are physically cut off of the stem. They also continue to grow as time goes by and can become rather large and scary structures.
The next sharp objects that plants produce are called spines. The spine is another structure that has evolved to protect certain plants from interlopers in the environment. The plants that most of us are familiar with that have spines are the cacti. Whereas spines can originate anywhere on the plant, they are found where leaves would be on a non-spiny plant. The origins of the spine are the same as a leaf and spines considered modified leaves. You may notice that plants like cacti have no structures that look like leaves and instead all the potential leaves are replaced by spines.
Finally we get to the prickles. A prickle is different in its origin than the other two. A prickle originates at random from the epidermal cells covering the stems of the plant. In the rose almost all of the prickles are located on the canes of the rose bush. Because of their superficial origin they are often easy to snap off from the stem. Roses, with very few exceptions, all have a lot of prickles, but the number can and does vary greatly from one variety of rose to another. One California rose hybridizer spent many years producing roses without prickles. He succeeded somewhat, and did market a number of roses with the first name smooth. The hybridizer was Harvy Davidson and there are about twenty or more varieties listed on the website helpmefin.com. Just use the phrase “starts with” and put in smooth if you would like to see these. Many of them are in commerce but none locally that I noticed. A few of the varieties are Smooth Lady, Smooth Delight, Smooth Melody and Smooth Perfume. I have never grown any of these varieties because the number of prickles on a rose plant in my garden was never an important factor in their selection.
So what is a rachis? In describing a rose leaf it is botanically a pinnately compound structure with leaflets originating from a central petiole. Because many words are often used interchangeably and correctly for structures in botany, this central petiole is alternatively called the rachis. However, the rachis is covered with an epidermis, just like the canes, from which prickles may and do grow. Whereas rose gardeners usually wear gloves to protect themselves against the large prickles that are present on most of the canes, they are not the only ones which can cause harm. These tiny prickles, as shown in the three pictures below from three random roses in our garden, while tiny in size and vary in shape can and often produce bloody scratches on my hands and arms when reaching into a bush for various reasons while not wearing protection. So, always beware of the large prickles but beware of the tiny ones as well. They are almost too small to see but they are big enough to be felt.
Photos by Rich Baer