PHYLOSIANS

Planet of Origin: Phylos, on the edge of the galaxy
The Phylosians are a sentient species of mobile plants who developed a technologically advanced civilization. They have a naturaly long life span which they extended with their science. While they had not yet ventured much outside their hoemworld, they had developped theoretical knowledge of interstellar travel and had even devised a plan to build a fleet of large military ships to ensure peace in their interstellar neighborhood. Exposure to a staphylococcus strain of bacteria brought by a human explorer stopped their effoert and wiped out most of them in the 22nd century. By cloning himself, the explorer was able to cure the phylosians over the course of the next century.
Source: Star Trek the animated series "The Infinite Vulcan"