Anthropocentrism only add biases to our understanding of 'intelligence'… let alone of 'mind'… and buddhists tend to talk a lot about the mind.
Some animals display signs of intelligence close enough to ours that we can compare e.g. New Caledonian crows with 5-to-7 years old children (Causal understanding of water displacement by a crow)!
But the Theravāda school associates one of the six consciousnesses to plants: touch… Other schools might associate the "buddha mind" to all phenomena, including plants…
Here are a few articles and videos —food for thought— to (re)start thinking about 'intelligence' (which is not without consequences on A.I. or on our capacity to assess any potential 'alien' intelligence):
• video Plant Intelligence: Rethinking Thinking
• video Michael Pollan: A plant's-eye view
• video Stefano Mancuso: The roots of plant intelligence