Star Trek: The Animated Series, season 1, episode 7
The Infinite Vulcan
Summary
While visiting the newly discovered planet Phylos, Lieutenant Sulu picks up a walking plant, called a Retlaw, and is poisoned. The alien species that inhabit the planet, who are plantlike beings, approach and save Sulu's life, but kidnap Mr. Spock.
Summary from Wikipedia, CC BY-SA 4.0.
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