Herbarium Plant Pressing Protocol

A Step-by-Step Guide for Young Botanists

A herbarium is a collection of preserved plant specimens and associated data used for scientific study, research, and education. Specimens are typically collected, carefully pressed using a plant press, and mounted on acid-free sheets using a secure stitching method. This process is accompanied by detailed documentation of important information about the plant species, including the collection location, date, time, and habitat. Characteristics of leaf morphology, such as leaf colour, shape, texture, size, and stem features are also often recorded.

The primary purpose of plant pressing is to preserve specimens in a way that maintains their structural integrity and distinctive features for long-term study and reference, making herbaria invaluable resources for botanical research, conservation, and education. The practice of documenting biodiversity through preserved plant specimens has been in use for hundreds of years. Some herbaria, such as the Royal Botanic Garden Edinburgh Herbarium (RBGE), contain specimens collected as early as 1697. The RBGE houses approximately 3 million specimens, representing two-thirds of the world’s known plant species. In India, the Central National Herbarium, established in 1797, holds over 2 million specimens, making it one of the largest and oldest herbaria in Asia.

Herbaria are accessible to professional taxonomists, scientists, and amateur botanists alike, thanks to the simplicity and effectiveness of the preservation, storage, and cataloguing methods used in creating and maintaining these collections. To foster a love and understanding of nature in school children, our community outreach initiative was developed to engage them in exploring local biodiversity and using simple scientific tools to study it in a hands-on, scientific manner.   

Figure 1: a) Identifying local plants for collection (b) Plant press used for creating herbarium specimens (c) Pressed plant specimens

This post outlines the protocols we used for our community outreach initiative, The Green Hour, which inspires school children to explore local ecosystems through simple scientific methods. We also share images of preserved plant specimens collected by students from Government Primary School, Ralli, Kinnaur, Himachal Pradesh. While the protocol serves as a strong starting point for engaging beginners, it may require further adjustments if applied for professional purposes.

Materials Required

1. Plant press with ventilation boards

2. Newspaper or blotting paper

3. Cardboard sheets

4. Scissors and pruning shears

5. Herbarium sheets

6. Thread and needle

7. Labels and pen

8. Field notebook

9. Gloves (optional)

Collection of Specimens

Site Selection and Identification Choose a plant specimen from an appropriate collection site with permission if necessary. Document the location, habitat, elevation, date and time of collection, and relevant environmental factors such as soil type, moisture conditions, wind exposure, and human impact, among others, that influence the plant's natural environment. Examine the leaf morphology, including colour, shape, texture, and size, to improve documentation.

Selection of Plant Parts Collect specimens that include representative structures: leaves, stems, flowers, fruits, seeds, or roots if possible. Ensure a range of features is included to aid in future identification. The following guidelines may help ensure a high-quality sample is collected:

1. The specimen should be intact and free of physical damage (avoid samples with eaten or broken leaves, or signs of disease). While finding a completely perfect specimen may not be possible due to environmental or ecological constraints, aim for specimens where most leaves, stems, and flowers appear healthy, with at least a few undamaged leaves and flowers.

2. Ensure that the specimen includes the phyllotaxy, i.e., the arrangement of leaves on the plant.

3. For the same plant species, collect multiple specimens in different seasons to represent the plant’s annual cycle for herbarium collection.
   

Minimize Damage To prevent damage to the hairs on the stems and leaves of the specimen, vigorous cleaning or handling of the specimen must be avoided. Small insects that may get pressed along with the plant specimen offer researchers an opportunity to study insects associated with the plants, especially when they cannot access the actual habitat. Additionally, avoid over-collecting and be mindful not to disturb endangered species or rare habitats.

Pressing the Specimens

Preparation Arrange the plant on a sheet of newspaper or blotting paper, ensuring leaves and flowers are spread out to show both sides where possible. Roots can be trimmed or arranged flat if needed. Carefully fold the newspaper or blotting paper from all four sides to prevent the plant from slipping.

Layering Place cardboard sheets between layers of plant specimens to prevent them from sticking together. Alternate layers of newspaper and cardboard to facilitate even drying and airflow.

Use of a Plant Press Once arranged, place the specimens in the plant press and tighten it to apply uniform pressure. This ensures that the leaves retain their original size, and don’t shrink during the drying process. Finally, leave the press in a well-ventilated, dry and cool area to facilitate the drying process and prevent the growth of mould or mildew.

Drying and Monitoring

Drying Duration Specimens typically dry within 1-2 weeks, depending on humidity and the type of plant material. Check the press every few days, replacing any damp paper to prevent growth of mould and mildew. The plants may lose their original colour at this stage. This is quite typical and no cause of concern.

Maintenance Ensure specimens remain under consistent pressure during drying to prevent curling or shrinkage.

Labelling

Each specimen should be labelled with essential data, including:

• Scientific name (or genus if uncertain)

• Collection date

• Location (including GPS coordinates if possible)

• Habitat description

• Collector's name

• Any additional notes on the plant's appearance or condition

Mounting and Storage

Mounting on Herbarium Sheets Once the specimen is fully dried, carefully mount it on a high-quality acid-free herbarium sheet using simple thread and needle. To secure the specimen, first mark an appropriate number of stitching points with the needle. Pass the needle from the back, over the specimen, and then under the sheet. Finally, secure the specimen with a knot tied at the back of the sheet. Ensure that no essential parts of the specimen are covered and that it is properly held in place. Avoid using adhesive tapes, as they may damage the specimen.

Final Labelling and Filing Place the specimen with a final printed label in a protective case under stable temperature and humidity to prevent degradation.    

Figure 2: a) Using pruning shears to collect the plant (b) Preparing the plant for placement in plant press (c) Mounting dried specimen onto a herbarium sheet using a simple needle and thread

Conclusion

This community outreach activity can provide students with a hands-on opportunity to learn about biodiversity and the importance of preserving local flora. Through collecting, pressing, and mounting plant specimens, they will not only gain valuable knowledge about plant identification and conservation but also developed a deeper connection with their natural surroundings. The skills gained through this exercise will be invaluable for careers in environmental and biological sciences, and also provide a creative outlet, contributing to a well-rounded development.

Photo Gallery

You may also download this protocol for personal use using the link provided below.

SVF_Herbarium Plant Pressing Protocol.pdf

Download PDF • 82.28MB

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