The Rise of the Herbarium

There was nothing novel in the practice of pressing and drying plants, especially flowers. The oldest example of a plant preserved in this way consists of the twigs and leaves of an olive tree (Olea europaea) made from a bundle of olive twigs bound together by cords made from palm leaves that was discovered in 1885 in an Egyptian tomb. The plant material was placed in the tomb in about 305 b.c.e. and the herbarium specimen is held by the Royal Botanic Gardens, Kew, London. Travelers had been pressing and drying plants for centuries as souvenirs of their travels, much as modern tourists take and keep photographs. Pilgrims also picked flowers along their routes and, once dried between the pages of a Bible or book of devotions, these could serve as objects for meditation as well as reminders of their journeys. What was novel was the idea of preparing plants in this way for use as botanical reminders. Herbaria were, and are still, used to confirm the identities of plants collected in the field. A large modern herbarium will contain several million specimens. The world's largest, at the Museum national d'Histoire naturelle, in Paris, holds 9.5 million plants, and the second largest, the herbarium at the New York Botanical Garden, has 7.2 million.

Scientific herbaria were being assembled in various parts of Europe by the end of the 16th century. A century later they featured in many of the cabinets of curiosities that were fashionable among the nobility, and some natural historians possessed their own collections. George Clifford (1685–1760), a wealthy Anglo-Dutch financier, owned one of the greatest. Clifford owned a country estate, De Hartecamp, about 5 miles (8 km) from Haarlem, the Netherlands, where he had a private botanical garden and zoo, and where he assembled his herbarium. His dried plants are famous because on August 13, 1735, the young Carl Linnaeus visited Clifford, who then became Linnaeus's patron. Linnaeus wrote a full description of the gardens, hothouses, and dried plant collections in Hortus Cliffortianus (Clifford's garden), published in Leiden in 1738 with illustrations by the German artist Georg Dionysius Ehret (1708–70), who was the finest botanical illustrator of his generation. Ehret's illustrations were made into printing blocks by the Dutch engraver Jan Wandelaar (1690–1759).

Herbaria found several uses. A botanist who came across an unfamiliar plant might send it as a herbarium specimen to a colleague for identification. By comparing dried plants, it was possible to discover duplicates of the same plant but with different names, and the specimen labels came to include all the synonyms. Such uses were possible, however, only if the herbarium sheets were kept separate rather than being bound into books as had been the practice earlier. Keeping the sheets separate also made it easier to rearrange their order as new ideas about classification were developed and tested.

Keeping individual herbarium sheets and passing them from botanist to botanist generated a new problem of ownership. Botanists began to identify their sheets, not by writing their names on them but by printing the blank sheets with ornamental devices—cartouches, vases, medallions, and a variety of illustrations were used. They were called ornaments and their use began in the Netherlands early in the 18th century.

Today herbarium specimens are used in plant classification. A botanist who discovers a previously unnamed species first publishes a very formal description of the plant in a scientific journal, proposing a Latin name for it. In order to register that name, the formal description must conform to rules set down in the International Code of Botanical Nomenclature, and it must be sent, with a specimen, to the International Committee on Botanical Nomenclature, which is the body that establishes the rules. The preferred specimen is a herbarium plant, but there are certain plants that cannot be pressed and dried successfully. In those cases a botanical illustration is acceptable. Once accepted, the original specimen becomes the holotype or type specimen against which other plants are compared.