What is an herbarium specimen? An herbarium specimen also called a “collection” or a “sample” 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 valuable information.
Importance of herbarium specimens
Herbarium specimens are kept for centuries in depositories called herbaria (singular, herbarium). Herbarium specimens help botanists name, describe, and study plant species. Every plant species name or binomial (genus name and specific epithet) is published based on a single herbarium specimen located in an herbarium. Specimens are 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. For this purpose also the name of the collector and the number of the collection are cited.
(See 7-minute Youtube video, “Herbarium specimen collection and preparation” which was taken in Davie, Florida.”
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 is based on precedence. In precedence, each plant name goes back to an original herbarium specimen although rarely for some species published centuries ago, a description may suffice.
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. The label 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 downloadable samples that can be used for labeling:
#1 – Herbarium specimen label template – increments collection numbers on a page of six labels (e.g., 33, 34, 35, . . .) and makes the collector and date the same.
#2 – Flexible specimen label template – only makes the collector the same on all six 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.
Note the non-obvious
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 (which will change with drying and storage)
- the height of the plant
- the microclimate 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
- presence of or damage by insects and other herbivorous species
- uses by humans including religious and medicinal uses
- 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, which 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 pickax, 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.
- flowers and fruits if present
- leaves and stems
- bark
- roots
- other underground structures such as rhizomes and corms
In the case of 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 complete 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 facing 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 cardboard, to help protect specimens and cardboard, and wick away some moisture.
Sequentially number of collections
Each collection of a single species at a specific 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. This makes possible 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 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. Repeat, fire safety. Pressing is important to prevent curling of leaves so a large stack may have to have its straps cinched tight 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 transfers 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.