What is the collection used for?
The Herbarium is used by professionals and amateurs from many walks of life for a myriad of purposes. Here is a description of the most important of these.
To identify plants
Have you ever tried to identify a plant? Was it easy? Being able to identify plants with certainty is a common and sometimes urgent task as the following examples show. Imagine a sick child being admitted to hospital after eating some berries; before deciding exactly what to do, the hospital must know what kind of berries (and consequently what poisons) were eaten. In another case police find seeds on a suspect's clothes and seek to discover from what plants they come as an indication of where that person had been. A phytochemist carrying out research in their laboratory using sophisticated equipment must have absolute confidence in the identity of the plant material being tested. Engineers or historians wish to know from what tree came the timber used to build part of an old ship. A strange new weed is found invading an agricultural crop and before deciding how to control it most effectively the farmer needs to know what it is. And wouldn't you like to know the name of that lovely fruit you ate on holiday in Asia?
In temperate countries the number of plant species found growing wild is comparatively low; around 1,600 species are recorded from Great Britain. Botanists in Europe have been studying their flora intensely for hundreds of years and our bookshops are full of field guides with pictures and photos and simple diagrams. This may give the illusion that all plant identification is straightforward, but the situation is very different in tropical countries, where the biodiversity is not only vastly more diverse but also far less known; so that we cannot even say how many plants there are. For example, botanists guess that in Brazil there are about 60,000 different plants; while current estimates of the different plant species worldwide are between 350,000 and 420,000.
Given this enormous diversity and lack of knowledge of the plants in tropical countries, identifying a plant accurately can become a real challenge. Some illustrated field guides do exist for tropical regions but are seldom complete. Even reference books (without illustrations) will generally be incomplete and many years out of date. Flora Brasiliensis, for example, was the last attempt to list all of the plants in Brazil. It consists of 40 volumes and was published between 1845 and 1906 but contains only a fraction of the species that today are known to exist in Brazil. The only way to identify a plant accurately, therefore, even for professional botanists is by careful comparison of the plant they wish to identify with specimens in a herbarium. The herbarium acts as a walk-in book - you turn the pages by moving from cupboard to cupboard.
To certify plant names
When finding a plant that is new - i.e. that is different from any plant described previously - a botanist will need formally to publish a description of the new species, saying how it differs from all others and giving it a unique scientific name using the Latin binomial system. The plant known in Britain as the broad bean is called haba in Spain and fêve in France. Linnaeus gave this plant the scientific name Vicia faba and you will see this name used in seed catalogues generally written 'Vicia faba Linnaeus' or more commonly in abbreviated form as 'Vicia faba L.', thereby confirming that they refer to the plant as originally described by Linnaeus in a publication in 1753. You can read more about plant nomenclature in find out more.
How do you prove what your own name is? You may be asked to show your passport or even to send a copy of your birth certificate. Nevertheless your identity may be stolen - increasingly common on the internet - or your name simply used by mistake. Plant names are no different and are often used incorrectly. Books, garden centres and particularly the internet are full of examples of one plant being called by the name of another. These errors have the potential for serious consequences as in the case of medicinal or poisonous plants for example.
So given the richness of biodiversity in the tropics and our uncertainty even about how many species there are, how do botanists meet the challenge of ensuring that a plant name is used correctly and avoid referring to some other plant by mistake? Once again herbaria provide the solution acting as the ultimate reference collection. In 1753, when Linnaeus first published the name Vicia faba as well as describing the plant that he saw, he published a list of the specimens that he was looking at and on which his description was based. These reference specimens are called 'type specimens'. A botanist looking at those same specimens centuries later knows precisely what plant Linnaeus was talking about. The name Vicia faba is thus fixed in time. Every one of the 1.5 million plant names published has type specimens stored in one or more herbaria. These type specimens are thus the jewel in the crown of any large herbarium collection - defining as they do for all time and in all places what a particular scientific plant name means.
The alert reader may ask why there are more than 1.5 million plant names when we estimate there to be approximately 350,000 plants in the world. The answer is of course that the same plant may have been described at different times by different botanists working in different countries. Once this duplication has been detected two or more names (synonyms) will refer to the same plant. There are many more plant names than there are plants. For this reason Kew and other organisations publish checklists which list all possible names, establish which name should be used for each plant and which names are synonyms of one another.
Given its age and global importance, Kew's Herbarium is particularly rich in type specimens with maybe 350,000 type specimens in the collection - which fixes for ever the identity of 350,000 plant names. It is these specimens, that are of most vital use to plant botanists around the world and it is these specimens that Kew is prioritising as we build this Electronic Herbarium Catalogue.
As a source of information about plants
A large collection of plants collected over time and around the world is an immensely valuable source of information about the plants contained therein. We can discover, for example, where the plant is found: in which countries and in which parts of those countries. We can compare where the plant is found today with where it was found 100 years ago and thus measure the impact of processes such as habitat destruction and global warming.
It is impossible to cover in a short space the myriad of purposes to which information derived from the collection is put. One frequent and important task, however, is for conservation biologists seeking to establish species Conservation Assessments for the International Union for Conservation and Nature and Natural Resources (IUCN). These assessments underlie policy and procedures for conservation efforts around the globe. Accurate assessment, however, depends on having up-to-date and comprehensive knowledge of a plant's distribution, which in most cases can only be obtained by looking at the herbarium specimens known to exist in major collections such as that at Kew.
You can obtain further information about the plant by measuring or observing its morphological characteristics under a microscope, by taking minute samples for analysis in the laboratory and by reading the information contained on the specimen label. Further data may be recorded in the collector's notebooks written in the field while the plant was collected, which form part of Kew's rich archive and which attract visiting botanists and archivists for research purposes.
Specimens of a species other than the type specimen help describe the morphological and geographical variation of the species. For example, a plant growing in the shade may look different from one growing in full sun. Identification of a plant requires such variation to be taken into account.
To validate scientific observations
Imagine that you are a world famous research scientist and have just made an exciting new discovery about the physiology, DNA, chemistry or ecology of a tree from New Zealand. Your laboratory methods are impeccable, your reputation very high and the publication appears in a well-known journal, but how do you prove your results to be genuine? How can other scientists and subsequent generations repeat your work and thus check your observations? How can your readers ever actually be sure about which plant you were writing? The only way is for you to take specimens of the individual tree on which you carried out the experiments and store them safely in a herbarium. In fact any reliable scientific journal will demand that you first deposit "voucher specimens" in a herbarium and cite these vouchers before publishing your work. So the Herbarium serves to validate all botanical knowledge and ensures the rigour and quality of scientific research and publication.
There are many many different uses to which a herbarium can be put and should you wish to learn more then you can read an article entitled '100 Uses for an Herbarium'.