We define pain as a neurological response. Since plants don't have nerves, they cannot feel pain. They cannot feel.

You argue the semantics in problem domains we don't fully understand. Feelings and sensations only get wishy-washy when you have a developed nervous system, because we cannot accurately predict how said system behaves due to its complexity. But we do know what is actually ascribed to that system, what behaviors it propagates as, and that things without it don't experience it.

We have vernacular in place to express how plants react to stimuli. Sensation, pain, and feeling are not in that vocabulary, because they describe an essential aspect of the animal kingdom, not the plant one.