Plotinus - The Enneads - Happiness in animals and plants
Type of Spiritual Experience
I'm not sure why he assumes plants have no feeling - they respond to light so they have feelings of a sort - nevertheless, the quote is a useful one. What may be missed fom the quote is that he says, good and evil are subjective and dependent on the observer.
A description of the experience
Plotinus – The Enneads
But, to begin with, it is surely unsound to deny that good of life to animals only because they do not appear to man to be of great account. And as for plants, we need not necessarily allow to them what we accord to the other forms of life, since they have no feeling. It is true people might be found to declare prosperity possible to the very plants; they have life and life may bring good or evil; the plants may thrive or wither, bear or be barren.
No! if pleasure be the term, if here be the good of life, it is impossible to deny the good of life to any order of living things; if the term be inner peace equally impossible; impossible too, if the good of life be to live in accordance with the purpose of nature.
Those that deny the happy life to plants on the ground that they lack sensation are really denying it to all living things.