Final answer:
In 'Avatar: The Last Airbender,' Iroh mistakenly made tea from a poisonous white jade plant, which he confused with the white dragon bush. This incident highlights the dangers of misidentifying plants, a valuable lesson about plant biology and safety.
Step-by-step explanation:
The deadly plant that Iroh made tea from in the fictional universe is the white jade plant, which is mistakenly identified as the rare white dragon bush. In reality, Iroh had brewed tea from a poisonous plant, which is a scenario presented in the animated television series Avatar: The Last Airbender. This show explores many fictional plants and herbs with properties relevant to the story. However, the dangers of misidentification and subsequent poisoning by poisonous plants are a real-world concern and can serve as an important learning point about plant biology and safety.