There are several species of plants that are poisonous to humans. Toxins are metabolites produced by plants to defend themselves against threats. The major poisonous principles present in plants are organic compounds such as alkaloids, diterpenes, flavonoids, tannins, cardiac and cyanogenic glycosides, proanthocyanidins, phenylpropanoids, lignans, nitrogen-containing compounds, resins, oxalates, and certain proteins or amino acids. Toxic plants are of forensic significance, providing evidence in suicidal, criminal, burglary, and other criminal offenses.