Thorns on a Swamp Rose

Over the brambles

The Swamp Rose lures me closer

Fingers hooked by thorns

A Haiku by Mark

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The Swamp Rose (Rosa palustris) is a perennial shrub that can grow up to 7 feet tall and is native to the eastern United States. As the name suggests, this plant prefers moist, acidic soil. The Swamp Rose flowers often grow to be about one or two inches in diameter and sparsely populate the stems.⁽¹⁾

In my experience the Swamp Rose often grows alongside blackberries and raspberries.  Both blackberries and raspberries are a part of the same family of plants known as Rosaceae.  As these plants compete for sunlight they intertwine with each other and create an almost impenetrable bramble.  

One common descriptor of a bramble is that it is a tangled mass of plants covered by thorns.  Well, in this case, the term “thorn” isn’t completely accurate for the spines that grow on the rose and blackberry plants.

The term “thorn”, which is generally used to describe an appendage coming off a plant for defense purposes, is actually a descriptor for a modified branch.  Botanists use the term “thorn” to describe the sharp and pointy appendage growing in places where a branches would be. Examples of plants with thorns are Hawthorns and some citrus trees. The other terms used to describe the pointy appendages on plants are Spines, Trichomes, Prickles.⁽²⁾

A Spine is described as a modified leaf.  They are also sharp and pointy but emerge in places where leaves should be. Cacti are a common example of a plants with spines.

Trichomes are those tiny hair-like appendages on plants that irritate our skin. Plants like Stinging Nettles have Trichomes.

Prickles are any sort of sharp pointed part of a plant that isn’t located where a branch or leaf would be.  Rose and blackberries have prickles.

The general consensus from researchers is that thorns, spines, prickles, and trichomes are defense mechanisms to protect plants from foraging animals.⁽³⁾  Some researchers have even hypothesized that these sharp appendages can protect plants from insects.⁽⁴⁾  However, in the case of roses, these prickles also have another role.

The prickles on a rose plant are often sickle shaped.  The unique shape of the prickle allows the plant to grow over, and cling to, other plants.(5)(6) This is a truly amazing adaptation if you think about it.  A wild rose plant will grow amidst many other plants and in the battle for sunlight they have these specialized tools that support their growth.  These prickles not only deter animals from eating their leaves and flowers, but also allows them to get a “leg up” on the competition. The prickles are like a plant version of climbing hooks.  That is pretty amazing!

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Now, returning to the discussion about using the term “thorn” to describe all the pointy appendages on plants.  In common language the terms thorn, prickles, and spines are often interchangeable.  If you use one of these terms in conversation, the other person will understand what you mean.  It is only when you start digging down into the plant morphology that it is probably necessary to know the differences between the terms.  

Then, just imagine, if we tried to go back and change all the places in poems, songs, and literature where people used the word thorn instead of prickle. I am specifically thinking about the Bret Michaels and Poison’s song, “Every Rose Has a Thorn”.  Imagine if that song was “Every Rose has a Prickle”.  It probably wouldn’t have been a hit.

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Do you have any favorite stories or poems about roses?  Please share in the comments below.

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Resources:

1. US Forest Service: Swamp Rose
2. Cornell-Laura Hlusko: Plant Defense: Thorns, Smells, and Flowers (PDF)
3. Wikipedia: Thorns, spines and prickles
4. Quanta Magazine:The Thorny Truth About Spine Evolution
5. Why do roses have thorns?
6. The LuEsther T. Mertz Library/Gardening FAQ