The plant is not just a thing in nature, but the miniature mirror of phusis (the nature of things), a synecdochic instantatiation of universal growth and its refinement in the faculty of the vegetal soul, the "lowest" and at the same time the most encompassing potentiality of all living beings.
The plant-nature synecdoche corroborates the sense of vegetal freedom, shedding a different light on the expression "to exist by nature," which in the case of the plant implies "to exist by itself."
If for a vegetal being existence by nature signifies, at bottom, existence by itself, then it is, in and as itself, ontologically free, liberated in the core of its being.