ABSTRACT
Although plenty of manuscripts are dealing with variability of EO components, only some of them are appropriate to formulate conclusions and optimize the quantity of different products.
The beginning this chapter presents examples for both quantitative and qualitative variability and explains why their characterization should take place at well-defined taxonomic levels. Then, sources of the detectable variability are presented, starting from traditional inheritance data till recent metabolomic studies. The significance of morphological and ontogenetic influencing factors is also presented by citing numerous good or even misleading studies. In separate subchapters, the variability aspects are discussed in connection with propagation biology, adaptation processes, and classical and up-to-date chemotaxonomy.
The chapter concludes that a simple summary of published data cannot reveal the biological variability of any taxa. Depending on pragmatic or scientific goals, for each of them different, carefully considered research methodology must be applied.
