6d ago

On trees...

182 comments

Are at least all woody plants related?
- As far as they are all vascular plants, but that's like, basically everything that isn't moss iirc.
  The evolution of wood is common because it's simple for cellulose to get denser in response to a need to grow taller to outcompete your neighbors.
  
  So trees are the "evolve to crabs" meme and wood is like a crab shell. Or, I guess just exoskeleton, because things that aren't crabs also have hard shells.
  
  Kinda! But the shell isn't what the carcinization memes are referring to. I'd say the biggest part of carcinization is the loss of crustacean tails. Basically every false crab is in the process of losing their tail in favor of a rounder body plan
  
  I was under the impression that structural lignin was what really made trees a viable style of growth, and that seems like an odd chemical for a bunch of unrelated plants to all evolve. Is there something I'm missing? Is lignin actually present in all vascular plants?
  
  I wasn't being specific enough. Cell walls in plants are composed of cellulose, hemicellulose, and lignin. Lignin IS one of the structural polymers that plants produce, and yea, every single vascular plant has and uses lignin to provide structure. Iirc its a polymer produced by every plant, including mosses and other nonvascular plants, it's just not used to the same extent.
  
  AH, I see. So, it already existed, but until trees evolved, it wasn't used to such an extreme extent.
  
  Yea, the evolution of vascularity in plants let them get off the ground in the first place (meaning being taller than a few inches). Vascularity is the first big jump plants made after leaving the water. From there, being taller means outcompeting your neighbors and spreading your babies further. When you have that double whammy of more food + more babies, you get a selective pressure for taller that never really goes away. This is why multiple families have species that have arborized and have continuously done so over their evolutionary history. If the niche is empty, something will jump into it, often sooner rather than later (on a deep time scale) which is basically the whole idea of convergent evolution as a whole.

182 comments