How Plants Are Classified

The Family Tree

All living things that humans know about are classified into the TAXONOMIC system which always uses Latin names so that people in different countries can compare their flora and fauna easily - a sort of international language for naming living things. The rules about naming things are very strict, but they are strict like a contrary-minded aunt who keeps changing her mind!

The living world is divided up as follows:

  Plant example Animal example
Kingdom Plants Animals
Phylum Spermatophyta Annelida
Class Magnoliopsida Oligochaeta
Order Magnoliidae Megadrili
Family Rosaceae Lumbricidae
Genus Rosa Lumbricus
Species Rosa canina Lumbricus terrestris
English Dog Rose Earthworm

Currently, the Family Tree of Living things (slightly simplified here by leaving all the Animals together, and not thinking too hard about life forms that you can only see with a powerful microscope) looks like this.

The Wild Flower Society is only concerned with the Pteridophyta (leaves, roots, good plumbing, spread by spores) and Spermatophyta (leaves, roots, very good plumbing, spread by seeds), though some people do have specialist interest in the Bryophytes (no plumbing, but do have leaves), Fungi, Algae andLichens (a symbiotic association between a fungus and an alga).

Taxonomy as a discipline is changing all the time, and species are continually being re-classified as science discovers more about them. It should be remembered that this system has been built up by naturalists for their own benefit, to make the job of understanding the living world easie. Even the strict idea of a plant species is something that people have developed to make it easier to understand the natural world, but it is an idea that works very well - it seems to match what we see and the way plants reproduce, most of the time.

The scientific name of a species always consists of two words, the first of which denotes the Genus that the plant is in and has a capital letter. The second word is the Species name, and this always starts with a lower-case letter. It is usual to either italicise or underline generic (genus) and species names when we write about them. In the family tree above:

Isoetes lacustris (Quillwort).

Equisetum fluviatile (Water horsetail)

Oreopteris limbosperma (Lemon-scented Fern)

Picea abies (Norway Spruce)

Rosa canina (Dog-rose)

Galanthus nivalis (Snowdrop)

In particular, the names of species and groups sometimes change because it is the rule to (almost!) always adopt the oldest known name that was properly written down by a scientist. Unfortunately this can lead to some plants having one or more names that have been used recently, which makes them difficult to look up in books.  For example bluebells used to be called Scilla non-scriptus, but should now be called Hyacinthoides non-scripta, because botanists have now agreed that the bluebells  really are different enough from the squills (genus Scilla ) to be in a separate genus, and the first botanist to say that they were, a long time ago, called the bluebell genus Hyacinthoides.  Similarly all the conifers used to be classed together as the Gymnospermae, but are now called the Pinopsida.

Families

The names of plant Families always end with the letters aceae All the plants in a Family share common characteristics, eg the Lamiaceae, or Dead-nettle Family, all have square stems and leaves arranged two-by-two up the stem, and most of them have flowers of similar basic shape and a definite smell.  Many books on wild flowers are organised by Family so if you can recognise what family a plant is in, you're half-way there to being able to identify it. Books will often put the families in the same order. For instance Ferns, Quillworts and Clubmosses come at the beginning of the book but Orchids towards the end.

Very similar species will be in the same Genus, which is like a sub-family. With practice it is often possible to tell what genus a plant is in just by looking at it - eg all roses (genus Rosa) look basically the same.  It is usually only possible to tell what species a plant is by using a hand-lens to look at very fine detail.  Latin names, though they may at first seem rather strange, do actually convey a lot of information very succinctly. Species names in particular sometimes tell you something descriptive about a plant, so for example, Lamium means deadnettle, album means white, purpureum means red, thus the white deadnettle is Lamium album and the red deadnettle is Lamium purpureum.  Sometimes plants can be separated even further into sub-species, but for the purpose of the WFS diary, these are not significant.

Colours don't always matter

It is fundamental to taxonomic classification that there have to be ways in which all the plants of one species are always different from all the plants of another species. If a plant sometimes has red flowers and sometimes white flowers, but there are no other differences between the red-flowered ones and the white-flowered ones, they are probably all of the same species.

But if there are other ways in which the red-flowered plants and the white-flowered plants are different, for instance if the red ones always have narrower leaves than the white ones, then they may be different species. Sometimes red deadnettles have white flowers, but they are still red deadnettles! Quite a few plants have a usual colour and a white variety but you can't make assumptions. Red Campion is a different species (Silene dioica) from White Campion (Silene latifolia) but blue, white mauve and purple Milkwort flowers can all grow together on the same hillside and are all Polygala vulgaris.

Confused?

Don't be - it's fairly straightforward in practice. Unless you're a real professional botanist you'll sometimes forget some of the names and classification. So just ask someone but remember that adults can be beginners too and some will know less than you do.

Happy botanising!