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A herbarium (plural: herbaria) is the collection of preserved plant specimens. Plants are dried, pressed, and preserved in sheets, and the sheets are sequentially arranged in a universally accepted way known as the Bentham and Hooker classification system. They are properly labeled with the following: the date the specimen was collected, the English name of the specimen, the family of the specimen, the name of the collector from whom the specimen was collected, the place where the specimen was collected and the locality name of the specimen. They are very useful for taxonomy studies as they are a quick reference source. The plants supply information on local flora and fauna that allows researchers to further locate wild varieties and their relatives.
The herbarium technique involves distinct steps in order to create a herbarium - collection being first, until deposit.
Collection
The first stage is the plant material collection stage. Certain characteristics determine whether they can be collected. Leaves should be fully developed and in a complete inflorescence state. Twigs should be thirty to forty centimeters long. Herbaceous plants with few or no woody parts are particularly harvested with underground parts. These collections are kept in polythene bags or metal vases to prevent moisture from escaping.
Drying
Collections are properly pressed against log folders; overlapping is avoided at all costs. The liners are kept safely in field presses which are changed frequently to prevent the plant material from rotting.
Poisoning
Poisoning is a crucial treatment as it ensures that microbes do not grow in the material. Mercuric chloride is generally used in this process. Mercuric chloride serves as an insecticide, disinfectant and fungicide.
Mounting, Stitching and Labeling
The specimens are again dried after poisoning and finally glued and sewn on the sheets of the herbarium. Usually, information is entered in the lower right corner of the sheet. Small paper envelopes known as fragment pockets are attached to the sheets to contain the flowers and the seeds.
Deposition
The arrangement of the sheet is determined by genus and classification. It follows the classification system of Bentham and Hooker, a system in which the Plant Kingdom is divided into flowering plants and non-flowering plants. Compounds such as dichlorodiphenyltrichloroethane (DDT) and copper sulfate are applied to it to kill insects like silverfish.
This technique dates back to the 16th century with Luca Ghini, an Italian physician and botanist. He founded the world's first herbaria, the first held in Pisa in 1543 and the second in Padua in 1545. These herbaria were within a university framework and were used to teach botany to students. They were tasked with ensuring the growth of the herbaria. In eight years, they managed to reach 300 documented plants in their first herbarium. Today, there are around 3,000 herbaria in over 165 countries with around 350 million specimens, the New York Botanical Garden Herbarium for example.
Ultimately, the herbarium technique is excellent and has proven to be considerably helpful in many ways. It provides important information on the morphology of plant specimens. Tags after the labeling process also help determine locality and taxonomy of the specimen. More importantly, the plant specimen is carefully preserved for a long period of time and this helps to advance the research.
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