It depends on how 'consciousness' is defined. If it just means responsiveness to the environment, it blends together with causality. After all, if you hit a billiard ball with a cue stick, the ball responds by moving. I have no problem with thinking that plants are part of the world of causality and hence 'conscious' in this extremely minimal (and probably misleading) sense.
A billiard ball has no sense of self and has no choice but to react in accordance to necessary laws of cause and effect. Consciousness represents an element of choice, however great or small, in accordance to the host. Consciousness introduces the study of "behaviour", or how (and if we are feeling ambitious, also studies of "why") an object "decides" to do something. In that sense, there are not many behavioural scientists in the field of bouncing billiard balls.
But we typically use 'consciousness' to mean something more than that. What that 'more' entails is rarely spelled out with any precision, it's much more intuitive.
Thats because its very nature is to sit outside of necessary laws. Just look at the rigours of falsification in physics compared to psychology for a comparison.
But it certainly suggests not only the ability to respond to particular aspects of the environment (causal linkage to them) but also the ability to extract information from the environment. (That's what our senses do.) We see this ability in the more sophisticated multicellular animals, both vertebrates and invertebrates. So these organisms become data processors and their behavior is more and more dependent on how that data is assessed.
And beyond that, for most people 'consciousness' suggests self-awareness. That's pretty mysterious since we haven't yet clarified what a 'self' is.
But it seems to suggest not only responsiveness to ('awareness of') causal properties in the physical environment, but also 'awareness of' the organism's own internal data processing functions. So there isn't just 'awareness of X', there's 'awareness that "I" am aware of X' or alternatively 'this is how "I" assess X'. I guess that I'd say that 'self-awareness' arises when an organism ceases only being able to respond to its external environment and becomes able to respond in a similar way to its own inner process as well.
What you are talking about here are the raw ingredients to step outside necessary laws (something not available in the toolbox of billiard balls)
Is it plausible to think that plants are able to do the latter? In my opinion 'no'. They lack any sign of the increasingly complex nervous systems that make it possible in animals.
Attributing the ability to circumvent necessary laws to a particular organ may work as a shorthand measure, but I don't think it can climb out of begging the question under further scrutiny.
Having a complex nervous system may make spotting consciousness more apparent, or enable a host to be more effective at circumventing necessary laws (and thus make it more obvious to us).
But that seems to say more about our limited powers to investigate the problem rather than ceiling limits of the problem itself.
For a long time mammals (other than humans) were also thought to lack consciousness since they lacked the high end estimations of human culture (eg science, philosophy, art, etc), so they were relegated to the status of billiard balls (despite exhibiting some clearly non billiard ball type behaviours .... imagine playing a game of billiards involving 16 fox terriers)