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Just had an unpleasant encounter with a wild rose. Not her fault, should've kept my distance.

Roses are some of the plants that have anatomical defenses (I'm talking about thorns). Well, what transpired was I walked into it and as I was leaving I felt the tug of the thorns. That is to say their morphology was similar to shark teeth (curved backwards towards the gut to prevent prey from escaping), which at some level means rose thorns are designed for a "similar purpose" (offense in a weird sense because roses are not carnivorous, instead of defense like e.g. cacti thorns).

Any good reason why this is the case? 🤔

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    $\begingroup$ The offense is to day that they are designed really. You probably meant to say that they evolved this way. $\endgroup$
    – CaroZ
    Commented Nov 12, 2023 at 19:24
  • $\begingroup$ @CaroZ, spot on! Why would rose thorns evolve like shark/python teeth instead of like cacti thorns? Turns out rose barbs are technically prickles. Do you know what the difference is between them? $\endgroup$
    – Hudjefa
    Commented Nov 13, 2023 at 2:40
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    $\begingroup$ I think the size of the thorns indicate the type of animal they defend against. Like a lot of plants have fur, which is like insect-sized thorns, but roses don't have fur as far as i know. so the thorns are probably mostly to prevent large herbivore predation. It doesn't seem to deter the deer in my backyard though, they're always licking the thorns with their tongues to get the juicy leaves. but probably for animals with weaker tongues, the thorns would be quite painful. $\endgroup$ Commented Nov 18, 2023 at 5:41
  • $\begingroup$ They are considered natural defense and they have evolved like that way only: birdsandblooms.com/gardening/flower-gardening/… and yes, thorns and prickles are different: huntington.org/verso/2020/07/spines-thorns-and-prickles $\endgroup$ Commented Nov 25, 2023 at 7:42
  • $\begingroup$ @NilayGhosh, interesting $\endgroup$
    – Hudjefa
    Commented Dec 14, 2023 at 12:33

1 Answer 1

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I think a good way to think about this is to analogize it to something closer to home. Imagine if someone approached you with the following hypothesis:

The tread on my tires is there to make sure the car doesn't slip when it moves. The bumps on my shower mat are similar in design and so must serve the same purpose. Does that mean that shower mats were originally designed to be mobile?

The flaw in this logic is clear. The common selective factor here is grip, not motion. The car needs grip to facilitate motion. The shower mat needs grip to hold your feet in place. They share common features because they are doing similar things but for a very different purpose.

Now think of that in reference to the thorns vs shark teeth question. The shark has curved back teeth so that its prey will get stuck on them, and they can't get away while the shark is chowing down without tearing themselves up even more. The rose also has curved back thorns so that they will stick into animal skin, but the rose isn't trying to hold you down. It just doesn't want you to eat it. But if it uses the same kinds of thorns then, likewise, an animal that gets caught on them is going to tear itself up getting uncaught, which is going to hurt more than it would if the thorn slid right out, making the animal even more averse to that plant in the future. Both sharp curvy barbs serve to get stuck in your skin and do damage on the way out, but the shark is trying to prevent you from moving, while the rose just "wants" it to hurt.

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  • $\begingroup$ Arigato gozaimus for the answer, but it still don't make sense to me. $\endgroup$
    – Hudjefa
    Commented Dec 14, 2023 at 12:32

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