There's no such thing as a tree (phylogenetically) (2021)

Summary

So you’ve heard about how fish aren’t a monophyletic group? You’ve heard about carcinization, the process by which ocean arthropods convergently evolve into crabs? You say you get it now? Sit down. Sit down. Shut up. Listen. You don’t know nothing yet. “Trees” are not a coherent phylogenetic category. On the evolutionary tree of plants, trees are regularly interspersed with things that are absolutely, 100% not trees. This means that, for instance, either: The common ancestor of a maple and a mulberry tree was not a tree.The common ancestor of a stinging nettle and a strawberry plant was a tree.And this is true for most trees or non-trees that you can think of. I thought I had a pretty good guess at this, but the situation is far worse than I could have imagined. CLICK TO EXPAND. Partial phylogenetic tree of various plants. TL;DR: Tan is definitely, 100% trees. Yellow is tree-like. Green is 100% not a tree. Sourced mostly from Wikipedia.I learned after making this chart that tree ferns exist (h/t seebs), which I think just emphasizes my point further. Also, h/t kithpendragon on LW for suggestions on increasing accessibility of the graph. Why do trees keep happening? First, what is a tree? It’s a big long-lived self-supporting plant with leaves and wood. Also of interest to us are the non-tree “woody plants”, like lianas (thick woody vines) and shrubs. They’re not trees, but at least to me, it’s relatively apparent how a tree could evolve into a shrub, or vice-versa. The confusing part is a tree evolving into a dandelion. (Or vice-versa.) Wood, as you may have guessed by now, is also not a clear phyletic category. But it’s a reasonable category – a lignin-dense structure, usually that grows from the exterior and that forms a pretty readily identifiable material when separated from the tree. (…Okay, not the most explainable, but you know wood? You know when you hold something in your hand, and it’s made of wood, and you can tell that? Yeah, that thing.) All plants have...