1. Identification of plant specimen for collection
The specimen to be collected is to be determined. As important is the location and season (if it is a vital factor)
2. Field collection
Plant selected for collection is assured of its health and adequacy of materials. They should be vigorous, typical specimens. Samples would need to be about 30 cm long and be as complete as possible (buds, flowers, seeds, roots and/or fruits) as well as a piece of stem bearing typical leaves. Should the leaf shape or size vary immensely on the plant, take several different pieces of different sizes or part that represent the variation.
Field data is also collected, information that are not recorded on the specimen. This practice would give accurate physical environment of its occurrence; identification of location, habit, vegetative type, associated species, its habitat, type of soil, elevation, temperature and climate at the time of collection. Date of collection and collector’s identification (ID) are also crucial information to be recorded.
Specimens are pressed as soon as possible after collection to maintain its original form before wilting. In the field, specimens are pressed flat between sheets of semi-absorbent paper for blotting such as newspaper, interleaved with corrugated cardboard or light plywood for better air circulation. The stack is then firmly strapped together in a plant press and left for dry. Several general hints for collection are making sure that bulky plants are cut, sliced or halved before drying and bushy twigs are pruned to get a flat and manageable specimen.
If on-site pressing is not possible, specimens should be wrapped with damp (not wet) papers and kept in loosely-packed plastic bags.
Small portions, detached fruits, flowers or even small specimens are to be safely kept in an envelope or specimen paper capsules.
In any circumstances, it is utmost important to tag each piece of specimen correctly and firmly.
3. Specimen curation
This is a process of extracting moisture from plants, in the shortest period of time, while preserving its morphological integrity. The method applied must essentially be simple and efficient with uniform heat distribution and a systematic application of pressure to prevent shrinkage. (6, 7)
Specimen should not be left in damp papers thus requiring change of drying paper every 2, 3 days during the drying duration of about a week, depending on the type / moisture content of specimen. The temperature should ideally be between 30-50°C.
Dried specimen will have to be devoid of any contamination in the form of bits of other plants, dirt and dead insects before mounting works are to be done. Specimen is arranged to fit the mounting paper, adjusted as necessary. Specimens that are longer than the paper size (rosette, grasses) will usually be bent into V, N or M shapes to fit the paper. If the specimen is too large, segments are mounted on series of sheets. Loose or odd fragments (inflorescence, seed, bark, fruit) are to be kept in properly labelled envelopes, attached with the main specimen.
Specimens are carefully mounted on the herbarium sheet using herbarium quality glue; strings and tapes when necessary.
A specimen label is to be pasted on the bottom right-hand corner of the herbarium sheet with information on botanical and vernacular names, locality, date of collection, elevation, collector’s name. It should also include the name of the person verifying the botanical name and date determined.
The key attributes to best preservation practice of herbarium specimens are temperature, moisture, ventilation and infestation control. Ideal conditions for would be at a temperature of 20-23°C, at a humidity of 40-60%, which are also ideal for staff efficiency. Adequate ventilation allows for air circulation which also contributes in prevention of the entry of humid air or dust and fungal infection, while avoiding loss of pest-preventive substances.
5. Duplicate Distribution
Each herbarium specimen will essentially have duplicates for several reasons,
The specimen would be made available to reach as many researchers as possible
Should the premise that housed the original specimen is struck by disaster (such as flood or fire), recipient herbaria would still retain the information and scientific data of the specimen
Duplicates that are not distributed will require higher safety storage space that is more costly and possess higher risk of deterioration (e.g. insect infestation, mould) particularly in tropical conditions.
General practice in herbarium specimen management is to distribute duplicates to more than one herbarium through an exchange and distribution exercise agreed upon by both parties.
A taxonomist or botanist is to be engaged in verifying or identifying a specimen. Identification is achieved using dichotomous keys; or published plant descriptions, illustrations, line drawings or photographs, and comparing with properly identified herbarium specimens. (1, 2, 3, 4, 5, 6, 7)
Bridson, D & Forman, L (eds). 1992. The Herbarium Handbook (Revised Edition). Royal Botanic Gardens, Kew.