In botany, a herbarium (plural: herbaria) – sometimes known by the Anglicized term herbar – is a collection of preserved plant specimens. These specimens may be whole plants or plant parts: these will usually be in a dried form mounted on a sheet but, depending upon the material, may also be kept in alcohol or other preservative. The same term is often used in mycology to describe an equivalent collection of preserved fungi, otherwise known as a fungarium.
The term can also refer to the building where the specimens are stored or to the scientific institute that not only stores but researches these specimens. The specimens in a herbarium are often used as reference material in describing plant taxa; some specimens may be types.
A xylarium is a herbarium specialising in specimens of wood. A hortorium (as in the Liberty Hyde Bailey Hortorium) is one specialising in preserved specimens of cultivated plant.