How plants excrete
A plant has no kidney, no lungs and no sweat. Yet plants excrete too.
Small openings in the outer layer of the stem. One of the routes by which gas exchange happens.
Pores in the leaves, each surrounded by two guard cells. This is the main route for gas exchange.
Through lenticels and through the stomata in their leaves, plants give out carbon dioxide gas in respiration and oxygen gas in photosynthesis. That too counts as an excretory process.
The same gas is waste in one place and food in another
In a plant, oxygen is the waste product of photosynthesis; yet that same oxygen is needed for respiration. Carbon dioxide is the waste product of respiration; yet that same gas is an input to photosynthesis. "Waste" is therefore not a property of a substance but a status relative to the process that produced it.
The fifth characteristic, complete
Excretion is the process of removing from the body the waste produced during metabolic activity — through organ systems in animals, and through pores in plants.