I searched the forums and was not able to find a link to a list of toxic plants for tortoises. I need to add some more vegetation to my year round outdoor Russian tortoise pen and don't want to have any accidents. Thank you for your time.

It's a non-starter. If the plant is toxic the animal won't eat it. They know way way way better than we do what is safe or not. I had a ten year battle with morning glory in my tortoise yard. It kept springing up every spring. The year I decided to quit fighting was the last year it grew. But grow it did, and the tortoises used it for cover, but NOT for forage. They somehow (smell?) know what is food.

In fact, don't you recognize food when you see/smell it?

I do. Natto is NOT food!!
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AMAZON REPTILE CENTER