An herbarium is a systematically arranged collection of preserved plant specimens and their associated data, primarily maintained for scientific study. Herbaria store a vast historical record of flora, offering a foundational resource for understanding plant diversity. These collections document the existence of species in a specific place at a specific time, providing a physical, verifiable record used across many fields of biology, ecology, and conservation.
Preparing and Preserving Specimens
The process of creating a permanent herbarium specimen begins with careful collection in the field. Collectors gather a representative sample, ideally including flowers, fruits, and vegetative parts, to show the full range of features necessary for identification. Field notes are taken immediately, recording location details, date, collector’s name, habitat type, and observations like plant size or flower color, which form the specimen’s label data.
The plant is spread out between sheets of absorbent paper and placed into a plant press to flatten it. Pressing is followed by drying, usually in a specialized oven under 50 degrees Celsius, which rapidly removes moisture to prevent decay and insect damage.
Once dried and flat, the specimen is affixed to a sturdy, archival-quality sheet of paper using glue or linen tape. Bulky parts, like cones or large seeds, are often placed in a small paper envelope, called a fragment packet, which is also attached to the sheet. The label is permanently attached to the bottom corner and contains all the collected field data and the scientific name.
For long-term storage, herbaria maintain strict environmental controls. Specimens are housed in specialized metal cabinets that shield them from light and dust. The storage area is kept at a stable temperature and humidity, often around 20 degrees Celsius and 50% relative humidity. Pest management frequently involves regular freezing cycles to eliminate insects that can destroy the dried plant material.
Managing the Collection Data
While the physical specimen is the primary object, the associated label data is equally important. This label information is cataloged and entered into a structured database. Modern herbaria use these databases to create a comprehensive, searchable record for every specimen in the collection.
Digitalization has transformed the accessibility of herbarium data. This involves creating high-resolution digital images of the mounted specimens to capture fine details of the plant structure and the label. The label text is also transcribed into the database, converting handwritten notes into searchable electronic fields.
This digitalization effort makes the collection virtually available to researchers across the globe, reducing the need to physically handle the original sheets. Scientists can access millions of specimen images and their corresponding data through online portals, supporting large-scale analysis of biodiversity information. This global accessibility is guided by principles like the FAIR data model, ensuring data is findable, accessible, interoperable, and reusable.
Research and Conservation Applications
Herbaria serve as a foundational resource for taxonomic studies. Specimens act as verifiable vouchers, providing morphological evidence for describing new species or clarifying relationships between known plant groups. Many specimens are designated as “type specimens,” the single reference point to which a species name is permanently linked.
The detailed location and date information on specimen labels allows scientists to map the historical and current geographic distribution of plant species. By comparing specimens collected over centuries, researchers can track how a species’ range has shifted in response to environmental changes. Herbarium data is also used to identify periods of invasion by alien plant species, helping to reconstruct their spread over time.
Specimens provide a unique time-series record for studying the effects of climate change on plant life, particularly phenology (the timing of biological events). By examining the collection dates of flowering specimens, scientists have documented that many species are blooming earlier now than they did decades ago. Furthermore, the preserved plant tissue can be used for molecular research, allowing for the extraction of DNA to study genetic diversity, evolutionary history, and population genetics.
This information directly informs conservation biology, providing data on past and present range limits. Data from herbaria can be used to model ecological niches, identify priority conservation areas, and support the compilation of Red Lists of threatened species. In some cases, seeds preserved within fragment packets on herbarium sheets can even be used for germination experiments to support recovery programs for endangered plants.