Prickles, Thorns and Spines, Oh My


I don’t know why I became obsessed over clarifying the difference between things on a plant that will draw blood, but it’s a rabbit hole I fell down that I thought I’d share with you. Perhaps it’s because the word prickle makes me smile, but I thought I’d clarify the terms for us.

Most of the time people talk about roses as having thorns, I’m certainly guilty of it, but in truth roses have prickles. Although I can’t really see Ann Bronte being as happy if she had to write, “But he that dares not grasp the prickles should never crave the rose” prickles are what stabs you in the finger or catches your hair or clothing whenever you’re working with roses. The word thorn is what all of us fall back upon when describing any kind of sharp projection on a plant, but if you want to use the correct term you need to determine where the sharp pointed structure you want to name is growing on the plant.

The term thorn applies only to structures that are modified branches. Just like branches do, thorns often grow out of a plant main stem at a leaf axil. The leaf axil is the point on the stem where a bud or leaf grows. Normally it’s the angle between the top of a leaf or a leaf’s stalk and the stem itself. The easiest and most obvious demonstration of a bud growing in a leaf axil is on the big mophead or lacecap hydrangeas. If you look at the base of each leaf, next year’s buds, nestled right up against the stem, are fairly obvious. This is the same spot from where most thorns grow. Japanese flowering quince have thorns, as does Pyracantha. Some citrus grow thorns, as do pretty much all gooseberries and hawthorns.

Prickles differ from thorns in that although they grow from stem tissue, they are extensions of its skin, much like hair, or fur on an animal. Thus, the above rose, and Aralia spinosa. Blackberries and raspberries. Thistles have both prickles on their stems and spines on their foliage. You can also have prickles on fruits, as you see on the fleshy seedpod of the Datura or horse and Chinese chestnuts.

If the sharp projection comes from a leaf or a leaf part, as opposed to a branch, it’s called a spine. Barberry has spines, as does black locust and the one you’re most familiar with is cacti, where what would have been a leaf has been transformed into a spine to help reduce the surface area and thus reduce water loss. You can also find spines on the margins of leaves, as with many in the holly family, as well as Mahonia. The hardy orange (Poncirus trifoliata), although a plant most aren’t that familiar with, has the most tremendous spines.

And yes, originally, all these sharp pointy bits evolved to help protect plants from predation, but nature never stays the same. I suspect that the real reason I got sucked into this educational vortex is a conversation I had with a client on the Jitney the other day who was under the misapprehension that plants that poke, stab and draw blood would be plants no critter would touch.

Unfortunately, this is most definitely not true. Exhibit one: Roses. I’ve seen roses eaten by both rabbits and deer, just as I’ve also seen deer munching down on wild (or escaped) blackberry brambles with no hesitation. Number two: Holly leaves can draw blood, but that hasn’t stopped our deer from stripping them from our plants has it? So, it seems that the herbivores of the world have evolved right along with the plants.

Camels chow down with relish on cactus for goodness sake. In the southwest there’s a rodent called the White-throated woodrat (Neotoma albigula) who, when given the choice, prefers eating a cactus with its thorns intact as opposed to one which has had them removed. The hypothesis being that cactus thorns are a denser source of nutrition.

So then what’s so cool about being spinescent? (Good word right? It means having or turning into or ending in a spine.) Well, the reason is that these sharp structures, while not entirely successful, can help prevent a plant from being eaten entirely. Yes, many herbivores have evolved with the ability to not just chew on, but also digest thorny material, but mature thorns slow the browser down a little. In Africa, the acacia tree is the giraffe’s favorite food. They browse on the spikes when they are young and flexible, and then later, when they harden and mature, the giraffe works around them to eat leaves and other tender plant morsels.

Where spinescence does work as a deterrent when it’s employed to create a hedge with the goal of becoming impenetrable. Osage oranges (Maclura pomifera) have spines, and before the invention of barbed wire, farmers on the great plains used the plant to contain their cattle. They gathered ripe fruits in buckets or barrels and left them outside over the winter so the seeds within would be scarified (a process that uses the cold to freeze and crack a seeds coating, thus aiding it in germination.)

Come spring the rotten fruits have become mushy and broken down, but still need to be broken down further so the seeds separate. It smells awful so you really need to wear gloves for this part. Once that’s done you add enough water to create a slurry, as liquid (I’ve been told) as pancake batter – it needs to pour easily and not clump up. A trench is dug and the “batter” is poured in and covered. Within a month sprouts start showing and farmers would transplant from areas where the plants were a little thick to spots where there were holes. They’d have to do this pretty quickly as the plants develop taproots once they’re older and won’t transplant as well.

According to a couple articles, some just let the hedge grow, but others would bend the young plants the following spring to create an arch following the line of the fence and “plant” the top of the sapling into the ground. This forces the plant to send up multiple side shoots that could then be woven together each year to create a more dense fence. (I do this bending thing with my roses, but without the tip planting. I learned it from a gardener at Sissinghurst by asking a billion questions as I watched them train and tie down their roses, and it really does work. Instead of getting long, whippy canes with blooms at their ends, the arched canes shoot out tons of shorter lengths each topped with a bloom. The following year you arch those too, and so on and so on.)

Look I started with roses, and ended with them. That’s got to be a record for me. The only thing I should have added was that the fruit of the osage orange is thought to have been the main food source of our now long extinct native Giant Sloth, but I can’t figure out what part of the sloth has prickles.

Paige Patterson’s snowdrops are up three weeks early this year!