Genitum lars was a type of herb native to the planet Ominnus. It was grown by the natives in their sacred gardens.
In 2266, Leonard McCoy learned that genitum lars was the antidote to a plague that had stricken the planet Argylus. Since there was none on board the USS Enterprise, the ship had to make the journey to Ominnus, where McCoy and Spock acquired some samples after fighting off the natives. They returned with the antidote in time to save the Enterprise landing party and the natives of Argylus. (TOS comic: "Child's Play")