Distribution Compositae

The production of copious trichome resin products raises the question of whether or not these resins are adaptive. Various proposals have been advanced regarding the defensive role of such compounds and the link between their structural variability and the coevolutionary process. However, there is little evidence linking these compound s biological function to the fine detail of their structural variability. The extent to which the observed chemical variability is an expression of past selection for specific novel chemical deterrents rather than the product of near-random activation of alternative terpenoid biosynthetic pathways is not known. Thus, in looking at the diterpene variability within the Compositae, care should be exercised in automatically associating a discrete adaptive function with each novel chemistry. 

Whatever the cause of the variability, chemical variation patterns correlate with taxonomic boundaries and may prove useful as taxonomic characters. Consequently, chemical differences between taxa may be useful chemical indicators of phylogenetic relationships. As a corollary, our understanding of the factors governing terpenoid biogenesis benefits from superimposing a plant taxonomic framework on the discussion of diterpene distribution and the underlying biosynthetic diversity. 

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