If you don't understand consciousness, how to make it from first principles and how it works, then I don't think you can confidently say "this isn't conscious" about much.
We can explain plant behavior through known physical processes though.
We don't need to lean on consciousness nor other mysteries at all. Nor we do have to when a rock changes color as it gets wet.
And without this parsimony, then we could claim that any unexplained mystery underlies any well-understood phenomenon which doesn't sound like much of an epistemic standard.
You could just as well make the same argument about human behavior in a broad perspective. Not understanding every minute interaction in our brain is a fairly secondary point when the overarching themes are all the same.
You can not make the same argument just as well about human behavior.
You can observe that a human and a record player can both say "hello", but you can not make the argument from that that there is no way to disprove that a record player might wish to express a greeting to a fellow being.
A simple process can duplicate the outward appearance and effect of a complex one (an mp3 player can talk), and a complex process can duplicate the outward appearance and effect of a simple one (a human can crank a drive shaft), and neither of these means that one might just as well be the other. They don't mean anything at all by themselves either for proving or disproving.
Humans reacting to stimuli in largely similar ways to a plant, or even plain physical process like water filling a vessel or diffusion, neither proves nor disproves, nor even merely implies or suggests, nor even merely opens any doors to any room for doubts about anything.
It could be that there is no fundamental difference between a human and a plant and a toaster, but this observation about similar behavior provides nothing towards the argument.
Perhaps it's easier to explain what I mean by turning it around. Every point you've just brought up can be made for plants in the same way. Humans are not special in the animal kingdom, we're just dominant in this era. Other species held that role in the past and other species still will do so in the future.
Yes, Chinese room is a well-known way of building up a system that's capable of understanding something from parts that individually are not (even though it was formulated in an attempt to prove the opposite).
I find some irony in the mention of elan vital upthread - on the one hand, most people here wouldn't let themselves be caught dead believing in elan vital, but then switch to any thread discussing AI, or even cognition in animals (or plants, like here), and suddenly vitalism becomes the mainstream position once again.
Even if there's no hard measurable rule on the limits of what we consider consciousness, that doesn't mean that definition includes anything that exhibits chemical reactions.
Ultimately it's a bit of an inprecise human concept. The boundaries of what fits in there might be somewhat unclear, but we definitely things that intuitively are (humans) and aren't (plants, rocks) in this set.
To your point, we have a great understanding of human/mammalian injury and injury recovery. We know what proteins and structures cause blood clots and we can even manipulate them to help peoples blood clot better. We know about nerves and reflexes and nociceptors.
But if I cut myself, no amount of science can currently assess how much pain I feel or how much it bothers me.
Brains work with chemical gradients and hormones. There's no magic involved, we just don't understand the meta, and are probably incapable of doing so.
I like to think of this in terms of the information theoretic formulation of physics and the bounds placed on that by the holographic principle. For any system to fully represent another internally, it must contain more bits of information than the system being internalized. In other words, it must contain more matter and energy, or be physically larger. The brain expends an extraordinary amount of energy looking for patterns it can distill into leaky abstractions in order to build internal representations of reality without violating this principle. However, since the abstractions are leaky, our understandings are imperfect.
You also can't confidently say "this is consciousness", as the top level comment did. Even less so when it's in an alleged form that's so different from our only confirmed case.
Wikipedia article about Consciousness opens with an interesting line: "Defining consciousness is challenging; about forty meanings are attributed to the term."
Perhaps "consciousness" is just a poor term to use in a scientific discussion.
If you don't understand consciousness, how to make it from first principles and how it works, then I don't think you can confidently say "this isn't conscious" about much.