Diversity taxon numbers

In any case, a special dif culty in evaluation of chemical diversity seems to be that the range of divergence, the altitude of the differences most obviously cannot be universally accepted and applied, although there is a need for some kind of minimum criteria in de ning a chemical taxon as a separate one. In case of essential oils and volatile components, this question is maybe even more dif cult to answer than in several other secondary compounds, as essential oils consists of a huge number of individual constituents. How many compounds and which of them should be taken into consideration ... 

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