Phil Busey Agronomy
Consulting Inc.


Herbarium specimen collection and preparation

by Philip Busey   social icons twitter facebook youtube linkedin

Herbarium specimen collection and preparation.


What is an herbarium specimen? An herbarium specimen also called a collection is a pressed, dried plant or plant parts suitable for storage and future reference accompanied by a label with the collector's name, the number of the collection, and other important information. Herbarium specimens are kept for centuries in depositories called herbaria (singular, herbarium) and help botanists name, describe, and study plant species.

Importance of herbarium specimens. Every plant species name (genus and specific epithet) is published based on a single hebarium specimen in an herbarium which is cited by the name of the collector and the number of the collection. Revisions, monographs, and floras are also published about groups of plant species which may include the geographic or temporal distribution of plant collections, and for this purpose also the name of the collector and the number of the collection are usually cited.

If a future botanist intends to rename a plant species or transfer a species to a different genus, the original herbarium specimen is examined and cited in a new publication announcing the new or transferred name along with a citation of the original publication. A plant species is that which a botanist says is a species. Not all botanists necessarily agree on the names of species (there are "lumpers" and "splitters") but all use a common language and nomenclature (code for naming plants) which based on precedence. In precedence, each plant name goes back to an original herbarium specimen.

Because of the importance of herbarium specimens in botanical nomenclature (naming) and identification, and the value of plant specimens in biological documentation and learning plant traits, students of plant identification should practice making herbarium specimens.

The label. The herbarium specimen label is a permanent part of the specimen along with the parts of the plant and contains the collector's notes of the location, date, collector's name, and the sequential number. This information all comes from a collector's logbook and which is later transferred to a label associated with the herbarium specimen (see below). Normally the label would include taxonomic information--the family, genus, and species--however an herbarium specimen can be unidentified.

Click here for:
#1 herbarium specimen label template

Increments collection numbers on a page of 6 labels (e.g., 33, 34, 35, . . .) and makes the collector and date the same

#2 flexible herbarium specimen label template
Only makes collector the same on all 6 labels; does not increment collection numbers and does not make all dates the same

With widespread use of GPS equipment including smartphones and internet maps, the label should include latitude and longitude as well as geographic and political subdivisions.

Notes on the label should contain descriptive information about the plant and the context in which it was growing that may not be visible later. Descriptive information can include the color of the fresh flower as that will change with drying and storage over the centuries, the height of the plant, the microclimate of where a plant was found growing, whether the plant was growing in the shade of other plants or near water, the type of plant community, the presence of or damage by insects and other herbivorous species, uses by humans including religious and medicinal uses, and the phonetic spelling of common name for the plant obtained from the people in the area in their native language. Herbarium specimens with labels are a rich source of data for future scientists studying the geography and natural history of plants.

The only information that is included on the label is the original information obtained by the collector, that would not be obvious from the specimen, and if possible the family, genus, species, and authorship of the species. Thus information obtained from other sources such as reference works is not included. Also, obvious traits that are preserved in the specimen, such as leaf arrangement, are not included in the label.

What to collect. The plant collector should attempt to collect a plant sample containing distinctive parts such as flowers and fruits if present, leaves and stems, and roots and other underground structures such as rhizomes and corms. Hand clippers, a pick ax, and other instruments are helpful depending on the type of plant. Collectors must respect property rights and protect plants that are rare. In some cases only a fragment of a plant can be collected, in other cases a collection cannot be made but a photograph might be taken.

In the case of very difficult plants such as palms (Arecaceae), aroids (Araceae), and aquatic plants, special methods may be required for collection and preservation. For example, for a coconut (Cocos nucifera) the collector may place the fruit in a cardboard box or may cut a section of a frond.

Handling of specimens. A whole day of plant collection often involves collecting many plants from a region. Plants and cut plant parts are placed in plastic bags, preferably opaque white bags, to reduce water loss and reduce overheating until they can be brought back to a location suitable for pressing such as a flat floor or tabletop, which would often be done after dark when it is no longer possible to make collections. If multiple locations were visited during the day, usually plants from the same location would be kept in their own bags separate from plants from other locations.

Ideally the plant collector had a logbook (a "collection book") in the field to write down sequential collection numbers and descriptions, and the collection numbers would be transcribed to the folded newspapers at the end of the day as the plants are pressed. In reality, and because of the extreme seriousness of losing a logbook in the field, collectors often number their collections and enter plant descriptions into their logbooks at a base camp at the end of a day of collection, or transcribe this information into the logbook from rough field notes, at the same time as specimens are pressed into folded newspapers.

Sizes. A single fold of newspaper, about 10.5 x 16.5 inches when folded, is placed to receive the plant specimen. The sequential collection number matching the number in the logbook must be written on the outside edge of the newspaper, usually with the collector's last name, with an appropriate water indelible writing instrument. The fold of the newspaper is then opened to receive the plant or plant parts, which is placed on the newspaper to show some leaves facing up and some down. Enough plant material should be added to fill the page. The newspaper sheet is then folded closed. Each successive plant specimen in a folded sheet of newspaper is typically separated by a sheet of corrugated cardboard, about 11.5 x 16.5 inches. Ideally cardboard sheets should be cut with corrugations running across the short axis to reduce restriction in air exchange. Blotters are also used when available, inserted between the folded newspapers and the corrugated cardboards, to help protect specimens and cardboard, and wick away some moisture.

Sequentially numbering of collections. Each collection of a single species at a single location by a single collector is assigned a unique number. Sequential collection numbers are used throughout a collector's life. For prolific collectors, numbers may reach tens of thousands or even hundreds of thousands. If multiple collectors are involved, usually the logbook and sequence number of the primary collector is used. When a collector's logbook is filled up, a new logbook is numbered from the point where the previous logbook stopped. If there are multiple samples of the same collection (multiple portions of the same plant), they are placed in separate newspaper folds, for distribution to multiple herbaria. In this case, all specimens of the same collection are assigned the same collection number.

Drying. To prevent fungus growth, prevent defoliation, and preserve colors as much as possible, samples are folded and pressed in newspaper and are air-dried relatively quickly, within 24 hours if possible. Drying with a fan at room temperature may be sufficient for most thin-leaved herbaceous plants in an air-conditioned indoors. In humid areas, an external heat source with forced air movement may be necessary, however, this must be done carefully to prevent fires which have destroyed herbaria and other buildings. For succulent species it may be necessary to cut open the tissue (e.g., cactus pads) and even to add salt to speed up drying.

If there are a few specimens and the climate is dry they can usually be stacked on the floor with books piled on top for a day or two. If there are many specimens or if the climate is humid, they can be stacked in a pile up to about 6 feet tall with a piece of plywood on the top and on the bottom, and strapped tightly, and subjected to forced heat that would be directed through the corrugations. Pressing is important to prevent curling of leaves so a large stack may have to have its straps cinched tighter every two hours.

With the plants pressed and drying, the plant collector goes back to enter any additional data in the logbook. When plants are sufficiently dried they can be shipped to a central location for labeling from the logbook. Typically all shipments and transfer of herbarium specimens are done in newspaper folds without cardboards or blotters.

Label preparation. Typically the plant collector does not prepare herbarium specimen labels until reaching an office with a computer and printer or (in the old days) a typewriter. If the plant collector is associated with a major institution, the labels might be prepared after the collector and specimens reach the home institution. A collector in the field not associated with an institution might prepare and insert labels in the numbered newspaper folds for shipment to an institution. There are links above, at the top of this web page, to label templates that may help filling out information.

What not to do. Labels must not be attached in any way (neither staples nor tape) to the newspaper folds because the original labels are a permanent part of the specimen. Descriptive information must not be written on the newspapers because the newspapers will be discarded at the time specimens are mounted by gluing to a permanent ragstock paper. Do not glue or attach plant parts to a paper sheet unless this is done as the final exercise; for herbarium specimens intended to be distributed to institutions, the institutions prefer to do their own mounting. The only information written on the newspapers should be the sequential collection number and the collector's name. Do not turn in herbarium specimens with cardboards except on the top and bottom of a pile of specimens.