So there has been some discussion in recent years that plants may be intelligent in the sense that they are able to react to stimuli in their environment and actively adapt. There are a few notable experiments that can be interpreted as demonstrating that plants' actions sometimes go beyond simple reflex and could be interpreted as "remembering" or "planning". However, these interpretations are still in debate.

https://en.m.wikipedia.org/wiki/Plant_cognition

Plant life makes up about 99% of the bio mass on this planet. If we can't decide whether the dominant life form on this planet is intelligent, I think that shows that whatever intelligence may exist on other planets or galaxies will probably be so strange that we could be looking right at it and not see it.