From 2speccers2tools wiki

As Horrible Rectangle Island warmed up due to the high amounts of background radiation, new opportunities emerged as a new biome began to form. For some populations of Stalked Radioshrub, the warming climate allowed them to become even bigger than before, resulting in the evolution of the Radiotree. The trunk of plumbochitin that is used to support their large size has become think and column-like while the leaf-like lobes have become extremely large in size so the surface area to get in sunlight and spite is much greater than their ancestor or close relatives. Additionally, the Radiotree also still gets a good amount of their energy from radiation. To help support its great size, the root system their ancestor had started to rely upon more now goes deep into the substrate for support. Certain aspects of the Radiotree, however, have not changed at all such as the cell wall-like structures and the lead around their cell's nuclei to protect them from their own radiation still being present. Much like its ancestor, the Radiotree produces proper spores, which get carried by the wind a certain distance before landing somewhere else and becoming a new Radiotree. While the Radiotree thrives along the southern parts of Horrible Rectangle Island as the Montane biome formed, the colder temperatures of the Northern Tundra prevents them from fully settling there and so they only live along the southern fringes of the Tundra.