The borgia plant was a poisonous plant native to planet M-113. Library record tapes listed it as a carbon group 3 vegetation similar to the Earth nightshade family, containing an alkaloid poison with a chemical structure common to most M-class planets. It was not familiar to Stafleet officers, such as James T. Kirk.
In 2266, the M-113 creature, while physically disguising itself as Nancy Crater, blamed Crewman Darnell's death on his ingestion of a borgia plant. However, Spock discovered that peculiar red mottling on Darnell's face was not among the symptoms of borgia plant poisoning. Doctor McCoy subsequently assured Captain Kirk that Darnell could not have died of alkaloid poisoning. (TOS: "The Man Trap")