An herbarium is a facility where specimens of plants are maintained for the purpose of comparison with new plant species, study, and general reference. Herbaria can be found all over the world, with collections which vary largely in size; the largest herbarium in the world is at the Muséum National d'Histoire Naturelle in Paris. Herbaria are often attached to natural history museums and arboretums, but they can also stand alone.
In addition to plants, an herbarium often contains samples of things like lichens and fungi, which have historically been lumped with plants. Most samples in an herbarium are kept on sheets of white archival paper which are carefully labeled, with bulky specimens which cannot be flattened being stored in archival boxes.
Looking at the label for a plant should provide a great deal of information. The name of the person who collected it, along with the site where the plant was collected, are typically towards the top of the label. The scientific name of the plant is also listed, along with any common names, and the date of collection. General information like a description of the plant and any other notes will be included at the bottom of the label, as plants may fade or become damaged through years of storage.
Many plant samples in an herbarium are whole, including the root, stems, seeds, leaves, and flowers, but it is also possible to see sections of plants, especially in the case of large plants, shrubs, and trees. Some herbaria also include paleobotany references, such as historical samples of pollen and fossilized plants, allowing people to study the evolution of plants through the centuries. In addition to dried samples, an herbarium can also house frozen and wet-preserved samples.
Studying the samples at an herbarium can allow researchers to learn more about the history and evolution of plant life in a particular region. Researchers can also determine whether or not a plant is previously unidentified by comparing it with samples in herbaria, and herbarium collections may be used to compare the flora of various regions on Earth, looking at how evolution diverges and converges in response to an assortment of factors.
Visiting an herbarium can be quite interesting, for people who are into plants. The collections are often quite extensive, and some herbaria have a focus on a specific area of interest, like tropical plants, which can make a visit especially fascinating. Curators are often happy to show visitors around and to discuss the plants in their collections, and some are delighted to show off samples of historical interest, such as plants collected by Charles Darwin on his famous Beagle voyage.