Suggesting that there's enough ambiguity for it to be reasonable to assume ferns exist on the same level of consciousness or understanding of the world around them as cows is a bit of a weak argument. There's a pretty obvious difference between the two, and even if you believe plants can experience pain or distress in a meaningful way, it still makes way more sense to kill a carrot over a pig if you have the choice, making the two very clearly not morally equivalent.