What types of defensive chemicals are produced by Asteraceae plants?

The evolutionary success of the Asteraceae family is largely attributed to its diverse arsenal of secondary metabolites, which serve as defensive chemicals against herbivores and other threats. Unlike other orders in the core asterid lineage, Asteraceae does not produce iridoid compounds; instead, it utilizes a wide range of other substances.1

Key defensive chemicals produced by Asteraceae include:

• Polyacetylenes: These compounds typically feature cyclic, aromatic, or heterocyclic end groups.1
• Sesquiterpenes: The family is particularly noted for producing bitter sesquiterpene lactones.1
• Terpenoid volatile oils: These are often released by roots, such as in the genus Tagetes (marigolds), to kill plant-parasitic nematodes in the soil.1
• Alkaloids: These are found in various forms, most notably pyrrolizidine alkaloids within the tribe Senecioneae.1
• Latex: This substance serves as an additional chemical defense mechanism.1

These compounds function as part of the plant's strategy to deter predators and survive in diverse environments.1