The Phylosians were a technologically-advanced race of sentient plant beings native to Phylos. Generally a peaceful species, the Phylosians had aspirations to spread peace throughout the galaxy, although they later had a fear of those unlike them.
Using their medical technology, the Phylosians extended their already lengthy life span, but nearly all life on the planet was destroyed (and with it, their dreams of galactic peace) when Stavos Keniclius accidentally introduced a bacterial infection to the planet. He cloned himself in an attempt to bring Phylos and its inhabitants back to their former grandeur.
Upon the USS Enterprise's visit in 2269, the Phylosians discovered the Federation had brought peace to the galaxy, letting Keniclius's clone and a clone of Enterprise first officer Spock work towards saving the Phylosians. (TAS: "The Infinite Vulcan")