Preparing herbarium specimens
A herbarium specimen is a pressed and/or dried sample of a plant or fungus that can be stored for future reference. The National Herbarium of Victoria at Royal Botanic Gardens Victoria (MEL) houses more than 250,000 herbarium specimens of plants and fungi from Victoria. These specimens underpin the major role of Royal Botanic Gardens Victoria in collecting and documenting the state's flora, both native and naturalised species.
Why are herbarium specimens needed?
Classification is a dynamic, evolving science. Species concepts and species delimitations often change when new evidence becomes available. Consequently, the names applied to plants and fungi may change. Herbarium specimens enable previous identifications to be verified or altered when the taxonomy changes, unlike the situation with identifications based on sight records, where it is often impossible to establish the current name in the absence of a specimen. When a new species is named, its description is permanently linked to a herbarium specimen, known as a type specimen.
Herbarium specimens provide a permanent record validating the occurrence of a species at a particular locality and time. Specimens and the associated label data also provide a verifiable and invaluable source of information such as distribution, ecological preferences and associated species.
What makes a good herbarium specimen?
There are two main elements to a herbarium specimen: the label and the specimen itself. Different methods of preparation are used for specimens of plants, fungi, lichens, bryophytes and algae. Information required on the label is similar for all groups.
The information recorded on the label is as important as the specimen. Even though a specimen may have been well collected and carefully prepared, it will be of negligible scientific value, and in some cases impossible to confidently identify, unless accompanied by basic collecting data and field notes. In addition, legible handwriting on the label makes databasing much easier.
Essential label information
- Collector(s) name.
- A unique collecting number. The simplest system is for each collector to commence their numbering sequence with the number 1, and number their collections consecutively.
- Date of collection: e.g. 10 March 2009.
- Locality: place/area name, property name (if private land), description of location in reference to roads, road junctions and distance from nearest place/town name (e.g. Victoria, Errinundra Plateau. The Gap Scenic Reserve, Gap Rd, 3.9 km E of junction with Bonang Highway).
- Geocode: a latitude and longitude, MGA (Map Grid of Australia) coordinates or street directory reference (include the edition). It is helpful to indicate the source of the geocode, such as GPS or map, and the precision of the geocode (is it to the nearest 100 m, 1 km etc.). Also record the datum used.
Other useful label information
Note any information on characters and field observations that cannot be observed from the pressed specimen:
- Habitat: include a brief description of where the plant is growing (e.g.Themeda triandra grassland; grazed paddock; weedy roadside etc.) and a list of other plants growing in association, if known.
- Habit: record the growth form (e.g. tree; shrub; vine; herb) and height (e.g. dense shrub to 2 metres high; sprawling herb). For trees, record the bark type and extent (e.g. rough bark up to 2 metres on main trunk, smooth above). Bark type is especially important in Eucalyptus. Also record the colour of fresh stems, leaves, flowers (for plants) or pileus, stipe and lamellae (for fungi).
- Abundance: number of plants at site. Frequency in the area (rare, occasional, frequent/common or abundant).
- Substrate: for bryophytes, fungi and lichens, include a description of the substrate on which the specimen is growing.
- For algae, collecting labels should include information on water type (saline, brackish or fresh) and quality (such as muddy or polluted), as well as whether the alga is free or attached to a substrate.
Collect plants in flower and/or fruit. These are usually critical for identification.
- Make specimens large enough to present a fair sample of the plant, its manner of growth, branching and so on.
- With smaller plants, such as grasses, rushes, sedges, irises and lilies, collect whole plants (or a number of entire plants) including underground parts (i.e. bulbs, corms, rhizomes) still attached to aerial parts of plant.
- Specimens should be pressed when fresh (i.e. in the field). This results in better herbarium specimens, making them easier to identify.
- When pressing a specimen, carefully spread out structures (i.e. leaves, flowers) so that diagnostic features are clearly evident. Make sure that both the upper and the lower leaf surface are visible by turning over some leaves.
Bryophyte specimens (mosses, liverworts)
- Collect fertile material with capsules, if possible.
- Collect at least a 4 × 4 cm patch.
- Place collection in a paper envelope (never plastic) and air dry as rapidly as possible in a well-ventilated area. Do not press the specimens.
- Bryophytes can often be found growing intertwined. It is important to check carefully that capsules belong to the plant that they seem to be growing from.
- Specimens should be ample and represent different stages of development. For genera with small fruit-bodies (such as Mycena or Marasmius) collect at least 20 fruit-bodies. For larger genera (such as Agaricus or Cortinarius), aim for five to ten fruit-bodies.
- Avoid collecting over-mature specimens that are decomposing or have mould growing on them. Also avoid damaged or badly eaten specimens.
- Collect all parts of the fruiting body including the cap, stem and base.
- Very large specimens should be cut in half or in quarters to aid drying and to fit within the MEL fungi packets (21 × 12 cm).
- For fleshy macrofungi, where the appearance is much altered on drying, notes on the fresh form and colour should be made. Photographs are very useful in documenting fresh appearance.
- Specimens should be thoroughly dried, such as in a food dehydrator or drying cupboard, or by placing specimens near a heater. A flow of warm air is the important factor for good drying, and temperatures of 30–40°C are sufficient. Do not dry specimens in a conventional or microwave oven.
- Once dried, specimens should be placed in a paper bag or envelope, or in a resealable plastic bag. Resealable bags are useful for preventing rehydration of specimens, especially in tropical climates.
- For microfungi on plants, such as rust fungi and leaf spot fungi, prepare pressed specimens as you would for the plant. Ensure that features of the host necessary for identification (such as flowers or fruit) are also collected.
- Simply place the lichen specimen in a paper bag or envelope. Do not place in plastic bags. Dry in a well ventilated area, as rapidly as possible.
- Collect some of the substrate, such as rock or wood, but trim excess substrate.
- Terrestrial algae (such as cyanobacteria) can be prepared as for lichens.
- Aquatic algae can be temporarily stored in water from the collecting site for a couple days.
- Dried herbarium specimens of algae can be prepared by 'floating out', followed by pressing. With the specimen in a shallow dish of water, place a piece of stiff white paper under the specimens and then carefully lift out the paper with the specimen on top. Press between newspaper.
- Marine algae must be covered by waxed paper or muslin before pressing between newspaper (which otherwise adheres to the specimen).
- Spirit herbarium material is useful for all algae and essential for some. Fresh specimens should be fixed before being pressed or transferred to spirit. Commercial formalin (a solution of 40 per cent formaldehyde) diluted between 1/10 and 1/20 with the collecting solution, is the most commonly used fixative (Warning: formaldehyde may be carcinogenic and all contact with skin, eyes and air passages should be avoided).
- Spirit collections are preserved in 70 per cent ethyl alcohol with 5 per cent glycerin and 25 per cent water.
Before collecting any plant or fungal specimens, permission from the land holder and/or manager should always be sought. Permits are required to collect in National Parks. The Royal Botanic Gardens Victoria cannot accept plant specimens that have been collected without necessary prior permission.