Originally this was something which served as an organ and with time was adopted by chemists to refer to carbon based compounds. As a result of living things being carbon based it extended to which living things and material which resulted from living things; hence organic matter.

The latter half of the 20th century saw the word adopted by the anti-chemical movement to mean something produced without the use of manmade chemicals.


The species is the basic unit that we divide living things into and originally species were seen as clearly distinct from one another. What puzzled scientist was how species appeared in the first place? The answer was species evolved from other species as a result of a battle for survival; as carefully argued in Charles Darwin’s “On the Origin of Species by Means of natural Selection or, The Preservation of Favoured Races in the Struggle for Life”. As is often the case the answer to this question produced a second question; if species appear as the result of a gradual change from one species into a second, where does one species stop and the next start. This argument will keep taxonomist in work so long as there are species to classify!

Clearly this makes a precise definition of what a species is impossible and whether a plant belongs in a separate species to another is the result of a consensus being formed. This consensus though is not fixed and has to be open to debate.

Species is also the basic unit of plant and animal scientific names and the name of a species is the combination of both the genus and species names. The rules for how a species name is structured is defined by International Code of Nomenclature for algae, fungi, and plants (as it is now known) and this goes into great details; but some of the important rules are:

  • With in any genus no two species can have the same name or one that could cause confusion with others.
  • For plants; the species name cannot be the same as the genus it belongs in, unlike animal names. So Rattus rattus, the black rat, is a valid name for an animal but the style would be unacceptable for a plant.
  • Importantly the species is always begun with a lower case letter,
  • The genus should be written immediately before it (the genus can be abbreviated to its first letter if it does not risk causing confusion) and both the genus and species should be in italics or if not practical underlined.


This is a collection of very similar species and forms the first part of a plant’s scientific name. For example Alchemilla in Alchemilla Mollis and as such it is very important in the naming of plants. Ideally it would be best to have a clear definition as to what constitutes a genus and the International Code of Nomenclature for algae, fungi, and plants goes into great detail as to how a genus should be named. It does not though make any attempt to nail down what actually constitutes a genus and for a very good reason – you can’t. In practice it would be impossible, plants evolve into genera in what ever way evolution takes them and only much later to people come along and try to group them into genera, species, etc. In the end a genus is a collection one or more species which a consensus has been arrived at that they should be placed together because of there botanical similarities.

Phosphorus (P)

This is the second most important plant nutrient after nitrogen and important in its take up. Phosphorus is an important element in many of the complex compounds in plants which they need. For example it is one of only five different elements in DNA, the others being oxygen, hydrogen, nitrogen and carbon. Even with an adequate supply of nitrogen, plants cannot take up enough nitrogen if there is insufficient phosphorus. A lot of the phosphorus in soils is in an insoluble form and plants can only take up nutrients if they are dissolved in water, in addition there is a tendency for phosphorus which is added to the soil to be converted to an insoluble form in the soil. Phosphorus is more likely to be in short supply in acidic soils.

Potassium (K)

This has a range of vital roles in plants, thought the exact nature and extent of them is still not well understood. It is generally more likely to be in short supply in soils with little clay in them such as peat and sandy soils.

Nitrogen (N)

One of the main plant nutrients and used by plants to make all proteins, and therefore as well enzymes, chlorophyll and many other essential parts of plants. The amount of nitrogen available to a plant is often the factor which limits it rate of growth and its behaviour within the soil is a very complex one with the amount available to the plant changing constantly. Like all plant nutrients; nitrogen has to be in a suitable form for the plants to take up, as an element it is a gas making up approximately 80% of the air we breathe but in that form is of no use to plants. The important exception to this last point is the legume crops which have evolved a way around this.


These are chemicals plants use to grow and are often divided into macronutrients and trace elements. These terms are in themselves are of limited use as if the plant needs the chemical to grow, in however small a quality, its absence is going to cause problems. In practice the main ones are nitrogen (N), phosphorus (P), potassium(K), Calcium (Ca), magnesium (Mg) and sulphur (S). Of these the most important are nitrogen, phosphorus and potassium and they are the NPK referred to on packets of fertilizer.

Trace elements

This is rather a catch all term for a very large group of chemical elements which plants need, but in very small amounts. It is very rare that adequate amounts of them are not naturally present in the soil.