All plants are classified according to their relationships. Relationships are established by shared characteristics, especially of reproductive parts. The binomial system that we use today gives each plant a name in two Latinised words: the first is the name of the genus, and the second denotes the species. This classification method was largely due to the work of Swedish botanist Carl Linnaeus, later amended, is still accepted worldwide as the standard way to identify plants.

The Oxford Collins dictionary states the word herb means: (n.) a seed bearing plant whose aerial parts do not persist above ground at the end of the growing season; herbaceous plant. Botanists describe a herb as a small, seed bearing plant with fleshy, rather than woody, parts (from which we get the term herbaceous) In addition to herbaceous perennials, herbs include trees, shrubs, annuals, vines, and more primitive plants, such as ferns, mosses, algae, lichens and fungi. Many people are sceptical about the effectiveness of herbs used for medicinal purposes, but there is no doubt that herbs posses amazing powers. Each herbs has its own unique array of active constituents, many falling into the same family but with different proportions of the same constituent. Believe it or not, even the seasons, weather, soil type, time of day and phase of the moon may influence the levels of active constituents. A boom in herb research in the 1990 has opened up a small insight into the very complex world of herbs, their properties and knowledge that our forefathers possessed thousands of years ago.

Herbs have a complex chemistry and the ingredients of herbal medicines differ greatly from a medicine made from the entire plant or an isolated chemical found in the plant, each may produce a different effect (synergestic effect). An example is meadowsweet (Filipendula ulmaria), containing salicylates a substance much like aspirin. Meadowsweet contains healing properties plus buffering substances that protect the mucous membranes from the corrosive effects of salicylates. Salicylates on their own may be extremely toxic.

Each herb contains a wealth of active constituents that give the herb its different aromatic flavors and smells. Many herbs are subject to legal restrictions due to their potentially dangerous nature. Their use, formulation and sale are closely governed and fall into three categories:

*Poisonous therapeutic herb

*Herbs that may be hazardous as garden plants

*Herbs that have become pernicious weeds outside their country of origin

Restrictions on therapeutic herbs may apply to the whole pant or specific parts, preparations, or substances derived from it. Some substances that are extracted from certain herbs may be highly toxic and subject to strict control. The legal restrictions on cultivation of certain herbs may also apply to herbs in certain countries and are usually those plants that illegal drugs are produced from.