Question: I recently look at a question on this site that questioned if a “world tree” is feasible, [Would a 'World Tree' be feasible in real life?](https://worldbuilding.stackexchange.com/questions/48435/would-a-world-tree-be-feasible-in-real-life). If i remember correctly, it stated that one way to distribute and transport nutrients and other valuable needs equally would be the use of a heart and circulatory system. From my understanding, I would guess that the entirety of a tree would look similar, but would work extremely differently.

**why would a tree need or evolve a circulatory system, and what environmental pressures would lead up to such a tree?**

Also, this isn’t necessary and you do t need to answer this but if you could answer what the tree would look like with said circulatory system, then that would be greatly appreciated

Answer: 
Trees actually **do** have a circulatory system already. It's called the [Vascular System](https://www.britannica.com/science/vascular-system). It works rather well too because it can support trees much larger than we are and get nutrients up through the roots all the way out to the leaves to support new growth, and oxygen from the leaves all the way down to the roots to keep the entire organism alive.

In point of fact, even scaling up may not be so much of an issue as a 'world tree' is still going to have lots of leaves all over it, meaning that (unlike animals) it has a decentralised oxygen generation model so it can get oxygen throughout itself with less of a distribution network than animals, particularly those animals with lungs, need.

Nutrients are a bigger issue but the beauty of a tree is that the photosynthesis means that it's producing both food and oxygen over a very large percentage of its surface area (the leaves) so what needs to be distributed is both less in terms of variety, but also has to travel (on average) less of a percentage of the body length to get there. Also, trees don't have specialised internal organs to support, especially brains, that in their own right consume a large amount of the nutrients and energy collected. So, that means that more of the tree (again as a percentage) is dedicated to energy generation, again making it more efficient meaning that the circulatory system doesn't need to be as advanced as it does in animals, kilogram for kilogram.

Put simply, unlike humans that need systems for distributing oxygen, energy and wastes in and out of all parts of a body, a tree has a far more efficient distribution system that meets the simpler needs of such an organism.
As stated in other remarks, plants already possess [vascular systems](https://en.m.wikipedia.org/wiki/Vascular_plant). They also possess mechanisms for responding to stimuli and for cellular communication ([like this, for example](https://www.sciencemag.org/news/2018/09/plants-communicate-distress-using-their-own-kind-nervous-system)). But that's a long ways off from the sort of circulatory system found in animals involving muscles and a nervous system.

So, why might plant life evolve like that? Perhaps to combat the physical limits plants presently face in regards to gravity vs. size, or to combat harsh environmental conditions where the usual passive nutrient distribution isn't adequate. But it would cease to be a "plant" as we know it anymore. I imagine instead it'd be something between a tree and [sea anemone](https://en.m.wikipedia.org/wiki/Sea_anemone). But it could very well still appear as treelike as you want it to.