I do agree that plants, trees and fungi (student of Paul Stamets) are living beings.
But as the definition of sentience is as follows, from the free on line dictionary:
sen·tience (snshns, -sh-ns)
1. The quality or state of being sentient; consciousness.
2. Feeling as distinguished from perception or thought.
Can it be said that any of the three, trees,plants and fungi, have consciousness, perception or thought?
Do they "know" they are alive? That would be consciousness.
These actions require an actual brain and nervous system to carry out these functions, primarily feeling. Unless we also say "feeling" as an emotion, then it would in no doubt require higher functions of a brain.
Kindest wishes, Dave