Poison partnership?

I have read that many small animals have exploited the toxicity of Rhus radicans to provide some protection from their predators.

Is this true of some plants as well?

On a hike the other day, I came across large clumps of moss growing on a large poison ivy. I’ve never seen this before, and the moss was only on the vine. None of the surrounding trees or bushes.

Is this a typical scenario? I couldn’t find anything with my search skills. Does anyone know anything about this?

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One of the only places I’ve found Spanish moss on our property is on and around a huge poison ivy vine growing on a loblolly pine.

My theory is birds – they love the fruit of poison ivy, and was suspecting they’re potentially helping to spread the moss around as they go, just as they spread the poison ivy everywhere through droppings.

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Is there a source for the idea that small animals are using Poison Ivy for protection from predators? Or are they just using it as cover because it can be so dense? I’m curious on how that would work and what animals are using it since I’ve always been of the understanding that urushiol only caused an allergic reaction in primates. I’m not sure about the moss connections to Poison Ivy, I run into the most poison ivy in disturbed habitat edges and I can’t say that I can recall seeing lots of moss with it but perhaps that’s a difference of ecosystems

Yes. My brain on far too little sleep and focus. When I tracked back my hasty research, I realised that I had indeed connected the human (primate) toxic reaction with many descriptions about how the plant also protects small animals by its dense cover and root system. Erg. (Mt. Stupid is quickly in front of me once again. Sigh.)

So what’s the best explanation then for why the moss would be only growing so definitively within the plant’s boundaries?

it’s harder to speculate without seeing what you saw. we know that “if it’s hairy, it’s scary”. i would guess that a large poison ivy plant would have lots of hairy roots on the vine. assuming you’re not mistaking these roots for moss, then i would guess that the hairy roots provide a place for moisture to collect, which would then be a nice little microclimate for mosses.

there must be something out there that has this kind of relationship. i can’t think of an example off the top of my head, but it seems like this would be the basis for some pairs in companion planting. so maybe some kind of plant growing among Alliums, for example, might benefit from the Alliums repelling some common plant pests.

D’oh! Still stuck in Mt. Stupid basecamp. Sorry about that. Here’s what I saw:

And a closeup:

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are you sure that’s moss? to me, it looks like fasciation. something caused the plant to put out unusual vegetative growth instead of flowers. you can post this on the main site, and i’m sure someone will know of a pest or disease that would cause this.


Thanks. I think I’ll do that. I wish I had taken better pics at the time. I need to go back and see how it attaches to the vine (very carefully, I might add!).

My limited experience with faciations is that they have always appeared as really flattened structures. If it’s not a moss, maybe a gall? I’ve seen oak galls that go something like this.

Thanks for your feedback. If I get any answers, I’ll pop back to share.

More gall than moss?



For those who’d rather see a quick video clip explaining how this push-pull thing works, see from minute 4:15 here:

Bingo! Someone (thanks @pisum !) piped in with a reference and I think they’re right —and so were you.

Eriophyes rhoinus

Bonus? If this gets confirmed, it’s the first obs in my region.

What I love about this activity is that it confirms something I’ve always believed in, even when others have told me otherwise.

And that is?

It really pays to notice the weirdos.

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