Long ago, science recognized two plants: Philodendron Selloum and Philodendron Bipinnatifidum. It was later discovered that these are actually the same plant and the two were merged into one. Philodendron Bipinnatifidum, the name means “double, feathery split-leaves”, grows a tree-like trunk and aerial roots that grow towards the ground to anchor it as it grows. It sheds its lower leaves along the way, revealing its trunk covered in “Scars” that almost look like eyes. Most of the ones kept as houseplants stay pretty compact unless they are very old. Growing outside in suitable climates will give them their more treelike appearance and that’s why they were also called Tree Philodendron.
Philodendron Bipinnatifidum, Philodendron Xanadu, and a few others were already subdivided into their own group within Philodendron. This group was known as Meconostigma. In 2018, a team of scientists recognized that these plants were very different genetically from the Philodendrons they were lumped in with. Paired with the fact that they also grow trunks like trees and shed their lower leaves, the plants were then moved to their own new genus: Thaumatophyllum.
So now, the plant you may know as Philodendron Selloum is most accurately called Thaumatophyllum Bipinnatifidum and Philodendron Xanadu is most correctly called Thaumatophyllum Xanadu.