A herbarium is a collection of preserved plants stored, catalogued and arranged systematically for study by both professional taxonomists (scientists who name plants), botanists and amateurs.
The practice of pressing plants between sheets of paper and drying them has been used for around 500 years old. Thanks to this simple technique, most of the characteristics of living plants are visible on the dried plant. The few that are not (e.g. flower colour, scent, height of a tree, vegetation type, etc.) are put on the label by the collector.
A working reference collection
The specimens that are stored in the herbarium are a working reference collection used in the identification of plants, the writing of Floras (a description of all the plants in a country or region), monographs (a description of plants within a plant group, such as a family) and the study of plant evolutionary relationships. The most important specimens are called 'types'. This is a specimen chosen by the author of a new species as a reference point for a particular species.
A herbarium is like a library or vast catalogue and each plant specimen has its own unique information - where it was found, when it flowers and what it looks like. They can also be used to provide samples of DNA for research, as DNA remains intact for many years. It is usually used for evolutionary studies and is routinely extracted from herbarium specimens.
Preserved and mounted
Individual plants or parts of plants are preserved in various ways. The most common method for preserving plants in a herbarium is to press and dry them, and then mount them onto stiff card using glue, tape and stitching.
For some groups, such as lichens, fungi, mosses and some algae, the specimens are placed loose in paper envelopes (capsules) which are then attached to the stiff sheets of card.
More delicate or fleshy material is often placed jars of alcolhol which maintains their structure.
Large specimens of fruit, seed and wood are held separately, often placed in protective boxes to prevent damage. An additional collection of microscope slides contains large numbers of diatom collections.
More recently, a collection of silica-dried material has been incorporated into the herbarium. These specimens are used primarily for DNA extraction, enabling researchers to study the molecular properties of species.
Specimens are continually being exchanged and sent out on loan to other herbaria.