As with anything in biology, definitions are slippery little things that get harder and harder to pin down the more specific you try to be. I take endurance to have something to do with being able to experience extreme physiological stress and persist through a combination of physical and mental traits.
A formula might look something like this:
Endurance required = (Amount of Pain ^ coefficient of ability to suffer) * Time
As impressive as it might be for a 1,000 year old eastern hemlock to weather every climatological torment Vermont’s weather can throw at it, the tree still has no cognitive capacity to recognize pain and therefore suffer. Lacking sentience, hemlocks, and by extension plants, prokaryotes, fungi, and most animals, cannot summon courage, alter their behavior in the moment to overcome obstacles and press forward, and therefore cannot “endure.”