Philosopher Kenneth Goodpaster argued that consciousness is just a biological adaptation that helps some organisms meet their interests – and so it’s a strange thing to base morality on. Instead, our moral duties should be based around helping organisms meet their interests, whether these involve consciousness or not. And all it takes to have interests is to be alive: a plant’s interests are in having environmental conditions where they can grow as well as possible, finding enough energy to reproduce, and that sort of thing.
There are a lot of ways to base morality on something other than consciousness, but the point is that consciousness isn’t necessarily the be all and end all. We don’t need plants to be conscious to explain why we should treat them with respect. As philosopher John Rodman wrote: “ I need only to stand in the midst of a clear-cut forest, a strip-mined hillside, a defoliated jungle, or a dammed canyon to feel uneasy with assumptions that could yield the conclusion that no human action can make any difference to the welfare of anything but sentient animals.”