Mounting System for Herbarium Specimens
The purpose of mounting dried plant specimens onto herbarium sheets is to preserve the specimens by minimizing damage by handling. Mounted specimens are more safely handled and stored because brittle and fragile parts are supported, and all parts are secured against loss. A mounted collection provides a sound display of the specimen and the collection data for repeated examination.
Katherine Boyd Rankin
National Mus. of Natural History
NHB – MRC 166
Washington, DC 20560 USA
Tel (202) 357-4369
Photograph: Julio Gisbert
The system described here is appropriate for mounting vascular plants. Algae, lichens and bryophytes are “mounted” using other methods. An herbarium specimen is comprised of a pressed, dried plant specimen affixed to a thick sheet of paper. The collection information relating to the specimen is contained in a label. This method involves securing specimens to the paper with thin cloth straps backed with a water activated adhesive, as well as sewing with heavy-duty cotton or linen thread (Fig. 1).
Figure 1. Mounted herbarium specimen. Fragment pocket is indicated with arrow.
Materials Tools Supplies
- Alkaline buffered paper, 100% rag (pocket paper)
- Alkaline buffered white paper tape, 1in width
- Bone folder
- Brass weights
- Cellulose sponges
- Laboratory paper tissues
- Linen or cotton thread, size 8
- Mounting Paper, 100% rag, unbuffered, (caliper .012-.015)
- Paper clips
- pH neutral bond paper, 100% rag (for labels)
- pH neutral linen tape with gummed backing
- pH neutral paper board (for bulkier specimens)
- Polyester film
- Polyethylene bags, zippered closure
- Polyvinyl acetate emulsion adhesive, pH neutral or methyl cellulose
- Sewing needles, sturdy (embroidery/crewel suggested)
- Sewing scissors, sturdy
- Waxed paper
Positioning and Arrangement
- Carefully examine the specimen. Check for the presence of flowers or fruits. Select the better side to display as many features as possible.
- Determine if the entire specimen will fit on one sheet (always try to mount on a single sheet). Some of the plant material can overlap as long as the important features are not obscured. If multiple sheets are necessary to adequately represent the specimen, annotate the labels as follows: “Sheet 1 of 3”, “Sheet 2 of 3”, “Sheet 3 of 3”.
- Separate clumps of plants, spread them out, remove excess soil and keep the plants aligned in the same orientation (usually base near the bottom and apex near the top). However, not all specimens should be mounted with the heaviest and bulkiest section near the base. If all specimens are mounted using this orientation, the general storage becomes lopsided.
- Arrange the specimen on the sheet to expose as many of the diagnostic characters as possible (e.g., flowers, fruits, petiole attachment, upper and lower surface of leaves, etc.).
- Avoid crowding the specimen into corners or placing it too close to the edges of the sheet where the specimen may be more vulnerable to damage. Keep in mind that when the specimen is filed away and is stored in species and/or genus covers, which open from right to left, more pressure is applied on the left edge of the sheet.
- A specimen label, which bears the collection information, should always accompany a specimen and the specimen should not be mounted until a label is provided. Allow room for attaching the specimen label to the bottom right corner of the sheet. This is customary practice in herbaria world-wide and it allows for easy reading when kept inside the genus cover.
- Position the collection label in place with paper clips and arrange the specimen and fragment pocket (explained in the next section) on the page. Ideally the label should be completely adhered. If the specimen is particularly large and the label could become obscured by the specimen, attach the label only along the right edge, allowing it to be pulled back in order to view the specimen.
- Before affixing, examine the label(s) and check both sides for information. If information is included on the reverse side, photocopy it on alkaline buffered paper and mount it with the other label information or place it in the fragment pocket.
- When affixing the label, place a sheet of waxed paper over the label to avoid smearing the print when pressure is applied by hand or a burnishing tool.
- Mount other labels or annotations above the specimen label leaving some space in between. Place the most recent annotation at the very top. If there are no additional labels, leave space above the main label to place additional labels in the future. If there is no room directly above, affix additional labels as close as possible to the left of the collection label.
- Specimen tags, which bear the collection number, may be left attached to the specimen or be mounted on the specimen sheet. As an alternative, they can be removed and placed in the fragment pocket.
- Deteriorated labels or labels on poor quality paper should be photocopied or reprinted, using alkaline buffered 100% rag paper. Place the original label in the fragment pocket.
- Determine the correct size of a “fragment” pocket needed to accommodate what is detached or is likely to become detached in the future, and allow room for it on the herbarium sheet. The pocket size may vary depending on the amount of fragments. The pocket, which is adhered to the sheet, will hold specimen fragments, whole leaves, flowers, and small fruits that have become detached from the specimen, in addition to other items already mentioned. Every sheet must have a pocket, even if there are no loose parts at the time of mounting. Use pH neutral 100% rag folder paper for the pockets.
- Place bulky fruits that do not fit easily into paper pockets in small plastic bags with zippered closures which are sewn onto the herbarium sheet, space allowing.
- Segregate loose bulky fruits above a certain size from the sheet specimen to optimize storage space. Place the bulky specimen with a duplicate label in plastic bags with zippered closures and store in the “bulky collection” of the herbarium.
- To assure reunion of the parts of a single collection, duplicate the label and place it in the bag. Make a cross reference on both labels indicating each part of the collection, i.e., mark the sheet “bulky collection” and mark the duplicated label (placed in with the bulky fruit) with the sheet number of the specimen.
Mounting or attaching the specimen
- After the specimen is arranged on the sheet and space is ensured for the other items, place weights on the specimen to hold it in place while mounting. It is best to begin mounting a specimen from the bottom and working up. Unless the specimen is very thick, strapping is preferred to sewing because it requires less time and effort.
- Cut small straps of varying widths from gummed linen tape. The width may vary from 1-5mm. Thin straps are used on finer plant parts and thicker straps over heavier or bulkier areas.
- Moisten the gum-backed straps by running them over a damp sponge. It is very important to keep sponge and hands clean while mounting to avoid soiling the page.
- Place straps over most plant parts, taking care not to obscure flowers. Because flowers and fruits are critical structures for study they should not be obscured by straps; nevertheless, they should be secured.
- To secure the flowers, use very narrow straps, sparingly, and avoid covering up the reproductive structures. Always bear in mind not to conceal important features such as leaf tips, leaf bases, flower structures, small inflorescences, etc.
- Place straps approximately 8cm to 15cm apart (avoid over strapping) and wherever possible, place straps at right angles to the stems, leaves, flowers, and fruits.
- Allow about 7-10mm of the strap to extend on each side of the plant part that is being fastened, after snugly fitting the strap against the plant. The tip of a pair of closed scissors is a useful tool for doing this. It is important to have the specimen secure on the sheet to avoid the specimen sliding and abrading on the sheet.
Sewing is the preferred way to secure thick parts (e.g. woody stems, bulky fruits still attached to the specimen) and is generally done to provide extra security for heavier specimens.
- Sew large, leathery leaves or numerous, overlapping leaves, making certain that the stitch goes over the edge of the leaf to flatten and secure it to the sheet. Stitches should not be longer than 1-2in; and try to use existing holes in leaves to make the stitches.
- For extremely heavy specimens, adhere the herbarium sheet to a card stock (same size as the herbarium sheet), which will provide extra support to the specimen. Mount as usual, but using a stronger needle for sewing.
- For shattering parts and flyaway inflorescences, cover the specimen or parts of specimens with small pieces of polyester film and sew it over the specimen.
- Make stitches using a sturdy needle threaded with cotton or linen thread and knot it on the back side of the herbarium sheet. Use double strands of thread to provide extra strength. When all the sewing is completed, cover the knots with alkaline buffered paper tape to prevent the strings from snagging on other specimens during storage.
- Use adhering techniques only for affixing the label and the fragment pocket, never on the specimen or any of its parts.
- Archer’s solution has been traditionally used because is dries quickly and does not wrinkle the label. Because there are possible health hazards associated with using Archer’s solution, a water soluble, white, pH neutral adhesive or methyl cellulose is recommended instead.
Other techniques for mounting plants exist, such as directly bonding the specimen to the paper with adhesive. The method described here has been selected over adhering the specimen directly to the herbarium sheet because it is a completely reversible mounting process, and allows for the expansion and contraction of the plant specimen due to changes in environmental conditions.