Preparing a Herbarium: 8 Steps| Plant Taxonomy

The following points highlight the eight main steps to be followed for preparing a herbarium. The steps are: 1. Rules for Herbarium Plant Collection 2. Tools and Equipment’s 3. Identification and Classification Back at Home 4. Setting the Plants Up 5. Special Treatments 6. Drying Plant Specimens 7. Mounting of Specimens on Herbarium Sheets 8. Herbarium Organization.

Step # 1. Rules for Herbarium Plant Collection:

(a) Almost all natural environments are suitable for searching of plants for the herbarium. So, places, which could appear sterile and dry, must not be overlooked. Only native and naturalized plants may be collected.

One may rely on the richness of the flowers and plants, which grow on grasslands and prairies, but one may also find an interesting specimen during trips to the mountains, swamps, coast, woods or wherever the climate and the temperature are not too extreme for plant survival.

However, collecting on private property, or National parks, or private farms should be avoided. In such cases, it does require prior permission from the owner or local administrative office. Further, some species of plants are protected by the law. So it is not wise to pick them up from the environment.

Some rare plants are protected in the whole territory of some region or districts. It is the responsibility of the plant collector to get a list of the protected species and one should get permission to collect these protected species too. One can also substitute colour photographs for samples of the protected species.

(b) One should avoid collecting all of something and the last of anything i.e. in general, a good rule of thumb is to collect only a small set of samples from a large population. It is wise never to pick up an excessive amount of specimens of the same plant, especially if one does not see many of them around. It is advised to harvest the minimum number of plants one needs for classification and collection.

In case of annual plants, a similar guideline is usually well to follow, but for trees and shrubs, it is best to selectively trim a few pieces from different individuals so as not to damage, in any way, the long-term survival of any individual.

(c) The most important part of every collected specimen is the flower. So the best seasons for picking up plants are spring and summer. However, certain species show their flowers in autumn or even winter. Hence, the colder months should not be neglected for excursions.

At the same time a few plants have a very short blooming time, which one should keep an eye on to catch the flowering time. Some plants have short-lived flowers, which are deliquescent and will break up in pieces, unless picked early in the day and immediately pressed in the folder.

(d) The plants which one is interested in should be fresh and not wet (apart from plants which live in aquatic environments). The most convenient specimens to pick up are those, which seem quite dry, and lacking any trace of surface moisture.

For this reason, it is better not to look for plants during rainy days, or early in the morning. Also, the hottest hours during summer days should be avoided, as plants will not show their freshest appearance.

(e) While collecting annuals, one should attempt to gather roots, flowers and fruits. Some species may also require fruits or mature seeds for identification, as for example, Brassicaceae require fruits for identification.

One may bring along some small bags or envelopes to carry the seeds and other small separate components. Sometimes during some particular excursion, one may happen to pick up the plant when the seeds are not yet formed.

In such cases it is advisable to return to the same place some weeks later, hoping to find some newly grown seeds. Similarly, while collecting a biennial, both the first and second year forms are useful, but at least flowers are required (again, Apiaceae requires fruits). As for herbaceous perennials it is best to avoid taking the root system.

A small piece of the root, or a single bulb, may be necessary for proper identification in some groups (Poaceae, Liliaceae). When collecting members of Poaceae, Cyperaceae and Juncaceae, for example, it is advised to make observations regarding rhizome, the presence of which can be critical in the identification of the plant.

Many other groups may have stolons or rhizome, and while a piece of the stolon can easily be gathered, the presence of a rhizome in some other groups might better be just simply noted rather than collected. All dirt should be removed from the plant after collection as well as all the insects, spider-webs and foreign bodies attached to the specimens.

(f) When collecting trees and shrubs, reproductive structures are vital. Cones, catkins and similar structures need not necessarily be new. However, every effort should be made to collect fresh flowering and fruiting parts if possible.

Several species will actually flower before leaves are produced. Such individuals may be collected, but for proper identification m some groups (for example, Fagaceae), leaves and even mature fruits may be necessary.

(g) A herbarium with scientific merit usually relies on the plants, which grow naturally in a specific geographical area. So it is important to distinguish between the wild species from those, which have grown after human intervention, as for example some garden flowers or most cultivated plants.

Occasionally it has been found that a plant species previously introduced by man may continue to spontaneously grow outside its original artificial environment. In such a case, the plant can actually become a new element of the spontaneous flora and can consequently become part of a herbarium.

(h) When one picks up plants from the natural environment, one should keep in mind that the plants have to be fixed up on returning home and they will have to be classified too, in order to achieve a scientific value for the herbarium. These operations require a substantial amount of time.

Hence, one should try not to collect so many specimens that one cannot find the time to settle and study all of them. Further, during classification, o < i.e. may have to section and basically tear apart some flowers.

Hence, it is suggested not to pick up just one or two flowers of each species while looking for plants, otherwise one may be forced either to sacrifice every flower for the classification job or to simply give up the classification.

Step # 2. Tools and Equipment for Preparing a Herbarium:

The following are the essential items or equipment, which are indispensable for plant collection:

(i) Tools:

a. Bags:

The collected specimens should be put into a strong bag made of cloth or polythene or similar material (plastic, etc.)- The function of these containers is to protect the plants from damage during the outing. When collecting in plastic bags, the specimens should be folded to the correct length for a herbarium sheet and placed firmly, but carefully, into the bag. They should not be just dropped in.

This will prevent entangling of separate collections and there will be less damage. Later while emptying the bag, it should be turned upside down. The material should not be pulled out of the bag. This usually breaks up the specimens. It is preferable to use large bags rather than small ones, as there will be less damage to the plants.

If one collects large, heavy plants, it is best to put them into a separate bag as they may damage other more delicate plants in the bag. This is especially true for palms and large aroids.

To prevent significant wilting, plants may be wrapped in moist newspaper and placed in a plastic bag, which should be kept shaded. When mass collecting in tropical areas, this is not always feasible. Small delicate plants should be placed inside smaller bags.

b. Folder or Plant Press:

If the excursion takes place in summertime or lasts for two or more days, it is better to bring a folder of approximately 45×30 cm or more, or the plant may be pressed after reaching home, whichever may be convenient for the collector. However one should keep in mind that a good specimen is made in the field, not in the herbarium.

It is therefore necessary to keep in mind what one is pressing in the field and how it will look on a sheet of herbarium paper. The folder must be made of cardboard or some other strong stuff, e.g. aluminium, and it must contain some old newspapers. The folder can be covered with cloth and it should be closed with straps or belts, and a handle or shoulder- belt should be added for easy carrying (Figs. 4.1a & 4.1b).

The folder could be made in some different way too, for example a couple of plywood boards containing some newspapers and the boards can be kept together with some large rubber straps or ropes. Blotting paper can be used instead of newspapers, but the latter is much cheaper. The picked specimens must be arranged inside the folder between a few layers of paper, so that every plant has some paper on both sides.

The closed folder does not have to press the specimens too firmly between the newspapers. If the plants are fleshy, more newspapers are needed, and one can also add some additional cardboard inside the folder. A large waterproof bag can be carried too to carry aquatic plants and can be used to cover the folder in case of rain.

(ii) Camera and tripod:

In order to substantially enrich the quality of the herbarium, not only aesthetically, but also from the scientific point of view, one may take colour pictures of each plant in its natural environment. In that way the dried specimen can be placed together with one or more photographs, which can be particularly very helpful for bulky plants like trees or bushes, which obviously can not be entirely included in a herbarium.

Also the habitat of a plant can be well described with a photograph, taking care not to be too distant from the nearby bushes or trees. The suggested equipment is a 35mm single lens reflex camera, with a standard lens and a macro-lens, the latter very useful for close-ups of flowers and other specific features.

Also a tripod can be very important if many close- ups have to be made, allowing the camera to remain steady. A tripod can also alleviate the need for a flash, which may be used when taking pictures in low light, but has the disadvantage of giving quite unnatural looking images. The speed of print films can range from 64-100 ISO to 200 or 400.

(iii) Field notebook:

An important part of plant collection is recording of field data at the time of collection, which can actually increase the botanical knowledge of certain geographical areas. Hence, it is a good idea to write down, various information regarding the specimens one is picking up. These notes will not only help the identification of the specimens, but also can be compared and added to the current botanical knowledge.

For this, special types of permanently bound, pocket-sized notebooks are used. Each book should have at least one hundred leaves, which are serially numbered, and six detachable tags should be on each page, which have the same number. These tags are tied to the specimens of the same kind, which are collected at the same time and place.

The data such as the field number of specimen, date of collection, the locality, the habitat, the botanical name of the plant (if known), the flower colour, abundance, variations and the associated plants, the vernacular name and the uses if any are recorded in the field note book at the time of collection.

Field notes:

The following is a list of what one can record in the field notebook at the time of collection:

a. Collector’s name, associated collector’s name(s).

b. Collector’s sequential field number (must be unique).

c. Collection date.

d. Locality :

If possible one can include .the longitude and latitude and also a sketch map is useful.

e. Habitat and ecology:

Terrain characteristics, vegetation type, association with other plants.

f. Plant habit:

The overall size and shape of the plant (tree, bush, epiphyte, etc.) should be described.

g. Field identification (family, genus, species if possible).

h.Stem and trunk:

Height and diameter; colour, texture, thickness and hardness; the presence of thrones and spines.

I. Leaves:

Deciduous or evergreen; colour, texture and overall aspect; orientation; exudate or presence of glands.

j. Inflorescence and flowers:

Note of everything that could be undetected in prepared specimens; colour; heterostylous, monoecious or dioecious; different behaviour (open / closed) during the day; exudate or glandular; pollinators, etc.

k. Fruits and seeds:

size, shape, colour, texture; smell, etc.

l. Underground organs:

Take some samples or describe them (size and shape, tap root, tubers, bulb, etc.).

m. Scent:

Record any particular scent, especially of cut parts and flowers.

n. Sap or latex:

Note the colour, smell, consistency, etc.

o. Name:

The locally used name(s) may be recorded.

p. Uses:

The uses may be recorded after getting confirmed.

Step # 3. Identification and Classification Back at Home:

All collections should be identified and classified as soon as possible. Any seriously considered collection of plants must report the most exact taxonomic denomination for each specimen, along with the date and place of collection. The name one should apply to a collected plant is the scientific name, a Latin noun, which, represents the only denomination that unequivocally identifies the specimen.

To classify every plant one picks up, one needs books that will describe all the species (and hopefully the subspecies too) of plants living in the region of one’s interest. This kind of book usually includes only black and white pictures, often drawings, and focus on all the parts (fruits, flowers, roots, etc.) that can help to classify a plant. There are various books available for the classification of plants.

Some are very complete and expensive, others are handbooks reporting only a particular group of plants (e.g. from a certain geographical area, or from a typical habitat), while others acquaint the reader with every kind of plant with little or any limitations, but they may not actually cover all the specimens one may find during travels.

During identification back at home, one has to carefully examine very small and complex parts, like flowers, internal features and little seeds. One will need some very important instruments such as a magnifying glass, tweezers and a cutter for this purpose.

Good field notes enables one to recall height of the plant and other observations made while collecting. It is a good idea to record the number of sepals, petals, stamens and note the condition of the ovary. Whether, the corolla is sympetalous, or if the stamens are epipetalous, and also the nature of any zygomorphic condition may be noted.

Sketches of the flower made in the field are often extremely useful. It is also important that one finishes the classification work before the plants start to wilt. In fact to compare the specimens to the books descriptions, one must hold fresh plants. Otherwise the identification work could become very difficult and maybe wrong in the end too.

Using an appropriate manual, the family, genus and species of the plant should be identified, adding the author to the binomial. If it is a subspecies or variety, then the infra-specific name and authorship should be recorded as well.

Step # 4. Setting the Plants Up For Herbarium:

One of the most difficult steps while pressing a plant is gaining the right arrangement of the specimens in the herbarium, as when the specimens are placed into the press they will acquire a shape and appearance that will last after the drying process, and so be similar or identical to the specimen’s shape in the herbarium.

Because of size and thickness limitations, it will probably be necessary to remove certain branches, leaves and bunches of flowers, or to carefully section them. This delicate job should be carried out with the help of a knife and tweezers, trying to arrange the flowers in the best possible manner, letting them show the most natural shape and all their features.

During this process, care should be taken to avoid the elimination of relevant elements, especially those, which were important for the taxonomic classification. Any loose part may be kept inside paper envelopes, which will be placed on the same mounting sheet as the specimen. Each species should also display both sides of its own leaves.

If only one leaf is available, one may cut off a part, so that the other side can be observed. If there are more than one flowers available, one can arrange some to show the back of the flower also. Depending on the size of the herbarium folders, one will be able to dry more or less large specimens. Some plants will have to be cut or bent, due to its excessive size. A stem should be bent at an acute angle.

While arranging the specimens on the paper layers, various plants can be placed on the same piece of paper, but care should be taken not to superimpose two or more specimens upon each other. It is better to choose specimens of the same thickness so that the pressure on that layer will be equally distributed.

If rather thick parts have to be placed in the press, an uniform thickness may be achieved by placing some pieces of papers near the more thick elements, so that the layer with the plants will have approximately the same height.

Step # 5. Special Treatments:

Some particular group of plants must be specially treated to achieve a good drying and durability:

(a) Cactus and succulent plants must loose their high percentage of water before being put to dry. To do that they must be placed below some blotting paper sheets, on them a hot iron may be passed rapidly. That must be done a few times, always changing the blotting paper.

Before the iron treatment, the softening of the cactus can be aided by the immersion in boiling water for half a minute, taking care to avoid immersing the flowers. Instead of boiling water one can employ diluted acetic acid or strong alcohol (20 minutes) or formalin (1.5 parts formalin, 1 part water). Since, most cactus, are really bulky and fleshy, it is appropriate to just keep and dry sections of the whole plant.

(b) Some plants have tubers or bulbs as roots, and they must be treated before drying. As with cactus plants, a few minutes in boiling water softens the parts. Care should be taken to immerse in water only the roots that are to be treated.

(c) Many plants have some (or all) parts, which are so bulky that it will be possible to dry only a longitudinal section (e.g. of the stalk or the inflorescence). Hence it may be necessary to eliminate most of the internal parts and pulp, leaving the external features untouched.

(d) Conifers and heathers generally loose the leaves during desiccation. To prevent this the use of warm paper is suggested, adding some passes with a hot iron. It could be helpful to put the specimens in boiling water first, then drying them as fast a possible.

Before the drying process, the small branches and the leaves can be smeared with diluted liquid universal glue like Vinavil (glue used for plastic, wood, cardboard, leather, etc.).

(e) Many flowers change colour in some way during the dyeing process. This may not be any real trouble for the herbarium. But some flowers show a dramatic change, particularly some violet, blue and red petals. To prevent that problem it is vital to achieve a fast desiccation, with many changes of the paper sheets.

Other suggested methods are to put the drying plants in contact with salicylic acid sheets (the sheets previously wetted with a 1% salicylic acid solution). Another practice is to immerse the flowers in petrol (American equivalent : gasoline). Then they must be air dried and finally treated with the paper sheets as the other flowers.

(f) Some plants have rather fleshy flowers (some orchids, iris, lilies, etc.) that must be filled with cotton wool before being put to dry. Every time the paper is changed, the cotton wool should be replaced too. The parts can be dried separately and then the flowers may be reassembled with the help of gum Arabic.

(g) If the flowers are likely to stick to the folder and break when handled, one can detach them and dry them apart using tissue or non-absorbent toilet paper, opening their folders only when the flowers are well dry.

Step # 6. Drying Plant Specimens:

After identification of the plant, one must hurry to go on to the drying process. It is best to work in a dry and ventilated room, avoiding damp, which could easily harm the specimens. Flowers and other plant parts must be dried up into a peculiar kind of press.

It is not difficult to build a home-made press for that purpose, keeping in mind that what must be accomplished is to keep the specimens squeezed between layers of paper (newspapers or blotting paper), until they are totally devoid of the original content of water, that is dried.

As for the folder previously mentioned, the upper and lower parts of the press might be made of heavy cardboard or thick plywood or equivalent material. The specimens should be placed between the layers of paper, which should be pressed, by two pieces of wood. These two pieces must be held tight by putting some heavy body on top, i.e. bricks or large books (Fig. 4.1c).

It is important that the plants are put under sufficient pressure, otherwise more time will be required to achieve a good desiccation, besides they could be damaged by dampness and moulds. Every specimen in the press must be linked with its own written data. The best one can do is to use a tag for each specimen, which can be attached with a string.

As circulating air is very important to get the specimens dried in a short time, it is better to add some corrugated cardboard sheets between the paper layers, so that some air can penetrate and speed up the drying process. Corrugated aluminium sheets are even more effective than cardboard.

Bulky parts can directly be placed in contact with corrugated material to speed up drying. If no such material is available, the filled press size should be kept small. Instead of newspapers, some recommend the use of blotting paper together with tissue paper.

A more advanced kind of press might be built for an optimal drying of the plants. This press can be made with two wooden boards with screws and nuts placed at each corner. Turning the nuts, the two boards will come closer pushing together the paper with the plants (Fig. 4.1d).

The press should be exposed to a gentle heat source, avoiding excessive heat that will “cook” the specimens. If fire is the heat source, keep the press at safe distance to prevent fire starting on the press. The process of drying may be hastened with the aid of artificial heat like an electric heater. Sometimes it is also possible to exploit the heat from the sun. In this case the presses must be rather small.

Changing the paper is surely a very important step whose importance must not be underestimated. In the first three or four days, a paper change should take place every day. Then one can leave more time between two changes. If the change of paper is neglected, the plants will take more time to loose their water content, besides they could be damaged if the paper stays wet for a few days.

While changing the paper one must try to keep the specimens intact, besides taking care not to mix up the tags or labels with the name and the other information regarding the drying plants. Once a specimen has become dry and stiff, it can be placed into the herbarium.

Step # 7. Mounting of Specimens on Herbarium Sheets:

Once the specimens have been dried, they will have to be mounted on a strong mounting paper sheet to display the specimens and its data in the most clear possible way, and the specimens will be carefully preserved being attached to mounting paper.

Arrangement of Specimen on Mounting Paper:

It is very important that the plants be arranged properly so that one can immediately see all the main characters of any particular species. The best manner to place the plants on the mounting sheets is to align them with the right side of the page (or diagonally if space is required) and to have the heaviest parts and specimens at the bottom (Fig. 4.1e).

The longest specimens can be folded if that can prevent the cutting of the stem into pieces. It is better to leave an empty space at the borders of the mounting sheets.

One can either arrange the specimens (along with the labels and envelopes for small parts) in a regular way from page to page, or stagger the specimens at different positions on each sheet, so that each group of sheets will have a more equally distributed pressure.

Mounting Paper:

The best permanent support is good white or cream cartridge-type paper, in particular 100% rag or chemical wood pulp. The size for mounting paper can range from 42×26 cm. to 45×30 cm. One may even need larger sheets for some bulky specimens. The size of the mounting paper also may depend on the cabinet or box, which will contain the bundle of plants.

The most delicate mounted specimens may be covered with a protective sheet of translucent paper, which must be rather strong and easy to fold. This paper can also be used to cover only parts of plants, such as fragile petals (Fig. 4. 1f).

Small Envelopes:

Small paper envelopes can contain particular portions (e.g. seeds) or very small plants. When these envelopes are folded and glued to the sheet, it should be possible to open them flat and close them without clips. Besides they must securely hold their contents (Fig. 4.1g).

Mounting:

There are different ways to mount the specimens to the herbarium sheets:

(a) Strapping:

In this method, the specimens are strapped with linen or cotton thread, that are knotted on the reverse side of the sheet, where it is better to add some gummed paper to avoid contact with underlying specimens (Fig. 4.1h). Also gummed linen tape, like the one used by bookbinders, can be used.

It must be placed where the specimens have greater strength, avoiding covering delicate details such as flowers. This method, allows to remove, and examine the specimen every time needed, but will allow a certain degree of movement, which can cause some trouble.

(b) Gluing:

If glue is chosen to mount the specimens, water-based woodworking adhesive or library pastes or latex adhesives must be used, which must be applied quickly, taking care of not using an excessive amount. One can employ a brush or a nozzle applicator, otherwise the specimen (especially if it is a small one) can be put in contact with a plate full of glue then attached to the sheet.

Glued material should then be left under pressure overnight, covering each sheet with waxed paper and with drying paper. For aquatic plants only latex glue must be used for gluing the specimens, as these plants can take up water from the glue.

(c) Pins:

Specimens can also be mounted using small paper bands, which fix the plant to the sheet with the help of pins. The strip is placed on the stem (or other crucial parts of the specimen) and the pin joins together the mounting sheet, the stem and the strip, passing below the specimen (Fig. 4.1i). As for strapping, this manner leaves a remarkable freedom of movement for further examination.

Labels:

Each specimen must have a label on its own sheet. It is advisable to use permanent and water resistant ink (black or blue), otherwise a pencil can be used (medium lead).

The label should include the following:

a. Taxonomic denomination (at least family, genus and species).

b. Scientific Name:

In italics or underlined. If there is an intraspecific name it may be included.

c. Location:

Indicate, in caps, the country or place where the plant was found, followed by a colon (:). Then give the location where the plant was found so that, (a) the spot might be found by someone else in distant future, and (b) a person with a generalized road map could find the location again. Avoid such references as “hill near my house” or “front of grandfather’s barn”

d. Habitat:

Try to indicate where i.e. the locality where the plant was found. This can often be done, by noting the type of soil or rock, outcrop, exposure, or general condition where the plant was found. One can amplify this by indicating the associated plants. In some cases, elevation is useful. Likewise, a general statement about the abundance of the plant may be helpful, especially to those in the future studying plant distributions.

e. Descriptive Information:

Information about the plant that either cannot be seen or might be lost in the future should be recorded on the label. Some taxonomists add local common names if they learn them and local uses. Observations are often useful and can help future scientists better understand the plant.

f. Collector(s) Name(s) and Number:

All person involved with the collecting of specimens should be recorded within reason. Mostly the names of two to five additional collectors are recorded on labels. However, the primary collector’s name appears first and the collector’s collection number is reported.

g. Date:

The date the collection was made should be recorded on the label. One should avoid using 08/09/94 as in the United States this usually means 9 Aug., 1994 while in Europe this would mean 8 Sep., 1994. The taxonomic community has largely adopted the mode of giving the day of the month first, followed by month (first three letters if abbreviated and then without a period) and finally the full year (1994, not 94).

Step # 8. Herbarium Organization:

The mounted specimens must be placed in bundles, which could be kept together with the help of strings or straps. Besides it is better to have cardboard or millboard supports at top and bottom of the bundles, to gain further steadiness (Fig. 4j). Each bundle must have its own label so that one will be immediately able to recognize the contents of each particular group of specimens.

Depending on the number of plants in each bundle and on the criteria chosen when dividing the collected plants into groups, one may write down the geographic origin or the taxonomic level (family, genus, etc.) or whatever identifies every particular bundle. The mounted specimens are stored systematically in special wooden or steel cabinets with pigeon holes also.

The herbarium must follow a certain arrangement, which will give some logical and scientific order to the collection. There are various systematic arrangements that can be followed. In most of the Indian herbaria the specimens are arranged according to Bentham and Hooker’s system of classification.

One can also choose to divide the specimens by their families (or even genus) alphabetically, or else one can group them geographically. These collections of specimens should then be kept inside boxes or cabinets, which should remain tightly closed and dust-proof.

The best places one can choose for the herbarium should be safe from the danger of fire, floods and other accidents. The temperature should be around 20° C and the humidity should not exceed 60%, in order to prevent fungal infections. Adequate ventilation is required, especially if the herbarium itself has a high concentration of insecticide or fungicide.

A dry room is the best to avoid proliferation of insects and consequent damage. Naphthalene and Para dichlorobenzene (PDB) are chemical repellents often used for preventing infestation. They are however very effective only at high concentrations, which increases the risks for human health.

Other products, which have been used in large herbaria are, mercuric chloride, cresol and LPCP, but they are complicated to use, and the results can be dangerous to human health too.