It's funny you bring up "have no mental state", because there is a plant that scientists find seems to have some sort of memory:

https://www.sci.news/biology/science-mimosa-plants-memory-01...

> The scientists show how Mimosa plants stopped closing their leaves when they learnt that the repeated disturbance had no real damaging consequence.

...

> Astonishingly, Mimosa can display the learned response even when left undisturbed in a more favorable environment for a month.