Most herbs and spices are native either to the sunny Mediterranean region or the hothouse environment of the tropics: in other words ideal regions with plenty of light, heat and atmospheric moisture. These ‘pampering’ conditions cause the plants to produce excess quantities of primary metabolites (substances used to build all the plant organs), as well as secondary metabolites (substances that are not essential to their existence and without which the plants can function quite normally).

It is broad enough to denote all the characteristic traits of the plants it embraces and at the same time narrow enough to state all that is essential. It is noteworthy that one often encounters the names of the same families in the case of plants used as herbs and spices. That is because the related plant species and genera, besides having similar morphological characteristics such as the shape of the flower, inflorescence and type of fruit, also exhibit similarities in the chemicals they produce and store in their tissues; in the case of herbs and spices, flavouring and aromatic substances.

It is planted to form hedges, prevent erosion on steep banks and for its foliage and in non-fertile areas is valued because of its moderate requirements on soil fertility and moisture. It sprouts prolifically from stumps and also produces root suckers freely so that in parks it sometimes spreads to such an extent that it becomes a weed difficult to eradicate. It is readily propagated by means of cuttings and root suckers.

Besides essential oils, many herbs contain so-called garlic oils. These are the seasoning element of all members of the genus Allium and tb-ir characteristics are similar to those of essential oils. However, an additional distinctive trait is that they occur in the plant in bound form releasing neither flavour nor aroma. That is why onion and garlic can be stored in the pantry together with other foods without any danger of their being contaminated by the characteristic pungent odour. This is emitted by the plant only when its tissues are bruised (when they are sliced, diced or crushed), which releases an enzyme that causes the decomposition of the garlic oils accompanied by a pungent odour. The same is true of the so-called mustard oils present in herbs of the Brassicaceae family, e. g. in the seeds of mustard, leaves of garden cress, and roots of horseradish.

Spicy and aromatic substances are not present in all parts of the plant, as a rule, but only in certain organs. Most higher plants consist of an underground part (root, sometimes a bulb or rhizome) and green top parts (stem and leaves). Flowers are modified leaves and are usually arranged in inflorescences varying in arrangement.

Following fertilization these develop into fruits containing seeds. In herbs the term herbage refers to the green non-woody stems and foliage and the term bark to the outside covering of the woody stem (branch).