Allelochemicals, allelopathy and essential oils: A field in search of definitions and structure

The concepts of allelochemicals and allelopathy are revisited and a more refined definition of allelochemicals is proposed. This new definition is applied in the case of essential oils. To assess the pervasiveness of the terms in the relevant literature, I make a quantitative survey of the distribution of essential-oil-related research efforts in different fields. I also review the current research trends on essential oils as allelochemicals mediating plant-plant, plant-animal, plant-microbe interactions and I discuss the role of essential oils in shaping interactions between aromatic plants and microorganisms in the Mediterranean environment. Research dealing with the biological activity of essential oils, though providing substantial information, often lacks coherence and structure. As for essential oils in the Mediterranean environment, though aromatic plants seem to have a competitive advantage, their role is far from clear.