What is an herbarium?
An herbarium is a scientific collection of dried plant specimens called vouchers. Herbarium collections provide reliable records for the distribution of vascular plants and are the basis for most taxonomic publications regarding plants. Whenever you read a book that describes how to identify a plant, what kinds of places you might find it, where it is distributed in the world, and all the particulars of the plant's size, shape, colors, etc., the information has been taken in large part from herbarium vouchers. Herbaria are essential in the training of plant taxonomists, who learn to identify, name and classify plants.
How are vouchers prepared?
In order to make an herbarium voucher, the plant is pressed and dried. A typical method is to lay out the plant inside a folded newspaper and press it between two pieces of cardboard until it is dry. Usually several such cardboard "sandwiches" are piled together and held tight by straps. To dry them fast enough to avoid decay, the pressed plants are either heated or dry air is forced through the corrugations in the cardboard, or both. When the plant is dry, it is mounted on a sheet of stiff paper to which a label is attached. The label will typically include the scientific name of the plant, the location at which it was collected, the date of collection, and the kind of habitat that the plant was found in. The plant is often glued to the sheet of paper, or perhaps sewn to it.
How are the vouchers stored?
After the plant has been attached to a sheet of stiff paper and a label attached, the voucher is stored in an herbarium cabinet. Temperature and humidity are controlled and the cabinets must be insect-proof to protect the vouchers. The vouchers are sorted by species within the cabinets and the species are arranged within genera and genera within families.
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