I usually call them all “thorns,” all those sharp, pointed, stiff parts of plants that we usually become most aware of when they scratch, prick, or snag. Winter, with the absence of leaves, is a good time to look more closely at the branches and stems of the plants in Eliza Howell Park and to note the variety of “thorns.”
True thorns, botanically speaking, are modified branches. In EHP, they can be found on such trees as hawthorn (first picture) and buckthorn (second picture).
Thorns grow from deep in the woody structure of the plant and are not easily broken off.
Prickles are also sharp outgrowths of plant stems, but they tend to be shorter. And, because they grow from the outer layers of the plant, they are more easily broken off.
I encounter prickles in Eliza Howell most often in berry patches (and prickles account for most of my scratches). This picture is of a wild blackberry cane.
The plant that is most commonly recognized as having “thorns,” both historically and currently, is the rose. As in the French proverb (“No rose without a thorn”), the beauty of the flower is often contrasted with the hurt or risk from the thorn.
It does not sound quite the same to say it, but if we were to be scientifically exact, we would call roses prickly, not thorny. Rose “thorns” are prickles.
This picture is of the stem of a wild rose in Eliza Howell and the following one is of a garden rose.
Spines are not easy to find in winter because they grow from the leaves and fruiting part of plants and drop with them in the fall. They tend to very thin and, while they might bend, they are often very sharp.
Note the spines on the thistle.
I often warn field trip participants to be very careful when grabbing hold of a chestnut; the spines on the bur (outer shell) are sharp.
Thorns, prickles, and spines all seem to have similar function, to help protect plants from herbivores. They simply take somewhat different forms.
I do not propose that we stop using the generic name “thorn” to apply to prickles and spines as well as to true thorns. I find it of interest, however, to note their differences. It is another little insight into the fascinating variations that exist in the natural world.