Every plant family, genus, and species produces secondary metabolites of which these chemicals can be used as taxonomic characters in classifying plants.
Secondary metabolites refers to chemicals produced by plants for which no role has yet been found in growth, photosynthesis or reproduction. These chemicals are of many varieties and are classified in various classes. Each plant family, genus, and species produces a characteristic of these chemicals, and they can sometimes be used as taxonomic characters in classifying plants.
Unlike the primary metabolites that build plant cell, tissue and organs and are essential for living plant cells, secondary metabolites don't have a primary effect on the survival of the organism, which has not yet been sufficiently clarified. However, it is considered that it was the secondary metabolites contribute to the adaptation of plants to different environmental influences and thus enable the survival of the species. They have a role in the inactivation and storage of harmful products but sometimes assume the role of coenzymes or hormones. Furthermore, they protect the plant against herbivore and pathogens attacks and regulate the relations between plants (allelopathy). Some secondary metabolites are also considered as good chemotaxonomic markers. Terpenes and alkanes are particularly suitable for studying the variability of trees at interpopulation and intrapopulation levels. In our country they have been thorougly investigated only in Serbian spruce, Bosnian pine and Macedonian pine. Flavonoids are increasingly being used in the separation of species and lower taxonomic categories.