Plants bought from nurseries usually are very polluted with insecticides and fungicides. Many iguanas incorrigibly eat the dirt the plants are potted in, so I used to cover pots with 1/4 inch steel mesh. I had one who liked to go over to the pot, crane his neck to look over his shoulder at me, then dip in for a mouthful. He knew vey well that he wasn't allowed to do that. LOL I guess.
If you want to get him a hibiscus bush, plant it in your yard and wait four or six months to move it into the cage for demolition.
We had a parakeet who loved to nibble and eat our "airplane plant" without harm, but if you give one to an iguana, don't look away, because when you look back it will be gone.