Preparation of Herbarium Specimens

A comprehensive guide to collecting, preserving, and organizing plant materials

Key Highlights

Field Collection: Collect specimens at the right developmental stage with complete documentation.
Pressing and Drying: Immediate pressing with absorbent materials ensures proper preservation.
Mounting, Labeling, and Storage: Secure mounting on acid-free sheets and proper labeling are essential for long-term preservation and scientific study.

Introduction

A herbarium is a curated collection of plant specimens that are dried, pressed, and preserved for scientific research, taxonomy, and conservation. The process of preparing herbarium specimens is meticulous and requires attention to detail at every step—from collecting and documenting specimens in the field to final packaging and long-term storage. This guide consolidates reliable practices to ensure that your herbarium not only maintains the integrity of the plant material but also serves as a valuable resource for future research.

Field Collection

Planning the Collection

Herbarium preparation begins in the field. It is essential to choose a suitable location and ensure that you have any required permits if collecting in protected areas. Key considerations include:

Timing: Collect specimens when plants are flowering or fruiting to capture all necessary reproductive parts.
Tools: Equip yourself with pruning shears, scissors, a trowel, field notebooks, and appropriate storage materials (e.g., polythene bags and newspapers).
Documentation: Use a field journal to record detailed notes on habitat, soil type, weather conditions, and specific identification numbers for each specimen.

Best Practices in Collection

When collecting, ensure that you include all critical parts of the plant such as roots, stems, leaves, flowers, and fruits, if possible. Label each collection in the field using a unique field number; this annotation will be linked later to a more detailed description on the herbarium specimen.

Pressing and Drying

Immediate Care Post-Collection

Once you’ve collected the specimens, the next crucial step is pressing and drying. This process helps maintain the plant’s morphology and prevents decay:

Pressing Techniques

The purpose of pressing is to flatten the plant to preserve its structure. Use a plant press or improvise one using layers of:

Blotting Paper: Absorbs excess moisture and speeds up drying.
Newspapers: Serve as cost-effective alternatives; ensure they are changed regularly to avoid mold formation.
Cardboard: Used as a rigid support to ensure even pressure is applied.

Drying Methods

The pressing process can take from a few days to several weeks based on environmental conditions and the thickness of the specimen. Ensure that you:

Change the absorbent paper if it becomes too damp.
Keep the pressed specimens in a dry, well-ventilated area away from direct sunlight to prevent fading and mold.
Consider controlled drying methods like a low-temperature oven or microwave drying methods if uniform results are required, though traditional air drying is most common in herbarium work.

Mounting and Labeling

Creating a Durable Record

After the specimens have dried thoroughly, the next phase involves mounting them onto herbarium sheets. The sheets are typically made from acid-free or archival quality paper to ensure longevity.

Mounting Techniques

When mounting, place the specimen carefully on the center of the sheet. Use either approved adhesives or linen tape to secure the plant without obscuring its detail. Be cautious with glue as it may obscure delicate botanical details; linen tape is highly favored among botanists.

Labeling Essentials

Labeling each specimen is critical for scientific and reference purposes. Essential information to include on the label are:

Scientific and common name of the plant.
Date and exact location of collection (including GPS coordinates when possible).
Habitat description and altitude.
Collector's name and field number.
Additional observations about the condition and distinguishing characteristics.

Traditionally, the label is affixed in the lower right-hand corner of the herbarium sheet to provide consistency and ease of identification.

Preservation and Storage

Maintaining Specimen Integrity Over Time

After mounting and labeling, proper storage is necessary to protect specimens from environmental degradation, pests, and light exposure. Several measures can be taken:

Preservation Techniques

To ensure long-term preservation:

Store specimens in a cool, dry, and dark place. Temperature and humidity control is crucial.
Consider periodically freezing the specimens, especially when dealing with infestations or if pests are a known risk in your locale.
Use fungicides (e.g., mercuric chloride, after proper handling and safety precautions) or other pest control measures as needed.

Organizing and Storage Infrastructure

Group specimens logically based on a taxonomic or collection system such as Bentham and Hooker's classification. Utilize archival-quality folders, cabinets, or boxes that prevent exposure to harmful agents like moisture, pests, and direct sunlight.

Comprehensive Process Overview

Step-by-Step Guide to Herbarium Preparation

Stage	Description	Best Practices
Collection	Gather complete specimens ensuring parts like flowers, fruits, and leaves are intact.	Record site details, use a field notebook, and assign field numbers.
Pressing	Flatten the specimens using blotting paper, newspapers, and a plant press.	Ensure regular replacement of absorbent material to prevent mold.
Drying	Allow specimens to dry completely to lock in their structural details.	Use a cool, well-ventilated and dark environment, or controlled drying equipment.
Mounting	Affix dried specimens onto acid-free herbarium sheets.	Use adhesives or linen tape carefully to avoid covering key details.
Labeling	Provide detailed information about each specimen on a label affixed to the sheet.	Include scientific name, location, date, collector details, and habitat information.
Storage	Securely store the mounted specimens in a controlled environment.	Utilize archival-quality materials and monitor for pest infestations.

Additional Considerations

Ensuring Quality and Longevity

The process of preparing a herbarium is not only about preservation but also about accuracy in documenting botanical diversity. Ensuring that each specimen is accurately labeled with its collection details enables future researchers to understand historical botanical data and track changes in ecosystems over time. Maintaining regular checks for pest activity, environmental fluctuations, and mechanical damage will help preserve the integrity of the collection.

Herbarium specimens play a crucial role in many fields such as taxonomy, conservation biology, and environmental sciences. By following these detailed and systematic steps, you create a resource that stands the test of time and acts as a comprehensive reference tool for the scientific community.