Overstory #159 - Collection of Botanical Specimens
Necessity of collecting botanical specimens
In the identification of an unknown tree, a specimen is worth more than many words or notes. It is difficult to identify a tree solely from the notes written in the forest.
From time to time foresters need to collect some botanical specimens of the trees with which they work. If they do not know the trees in the forest, then they should preserve specimens for identification later or for shipment to a large herbarium or to a specialist for determination.
For example, on making an inventory of the forest resources of a region, numbers or common names can be used for the unknown trees. Then, specimens should be collected for later identification.
Systematic botanists have various methods of collecting specimens. However, foresters generally collect only a few specimens and can employ the simple methods. In an emergency a twig can be broken from a tree and pressed in a notebook, in the pocket, or in a book. But it is worth the trouble to collect good specimens and in the end the identifications will be better.
Instructions for making collections
Collect Sufficient Material of Good Specimens with Flowers or Fruits
This is the first rule. Frequently, botanists are interested in collecting incomplete specimens of rare plants, but foresters are not. A rare tree generally is unimportant in forestry.
It is very difficult to identify correctly and completely a sterile specimen of a tree from only the leaves and twigs. Trees in various families have very similar leaves. Nevertheless, often unknown trees are found with neither flowers nor fruits, and it is necessary to collect sterile specimens. Possibly there can be found a tree flowering outside the regular season. If not, it is very useful to collect a wood sample from the same tree. Perhaps specialists in wood anatomy can identify the genus or family of the wood, and then botanists can continue the identification.
Collect at Least Two Sets
Two specimens should be collected from the same tree, one to keep and the other to send to the herbarium or specialist for identification. Also, a few additional flowers for dissection will be helpful. Whenever convenient, it would be useful to collect more sets. However, more time is spent and more equipment is needed in preparing the additional sets. In order to avoid a mixture of two species, all sets should be from the same tree.
Write Useful Notes in the Forest for the Label
A specimen without notes is not worth much either to the forester or to the herbarium. In the herbarium the notes on the label probably are worth more than the specimen. These notes include:
- Name of the collector.
- Number of the specimen. Each collector should use a series of numbers for convenience in his notes, in identification, and in the herbarium when later reference is made to the specimens.
- Locality. The country, State, municipality, exact locality, or distance and direction from a city or from a point on the map.
- Elevation above sea level.
- Forest type. Associated species. Soil. Whether planted or wild.
- Common name.
- Size and habit. Height and diameter of the tree, or whether the plant is a shrub, vine, or herb.
- Other notes. Abundance. Color of the flower. Fruit. Bark and latex. Wood. Roots.
Naturally all these notes cannot be obtained for all specimens.
It is difficult to collect botanical specimens of trees because the branches usually are high. In a search there may be located a small tree of the same species or a tree with low limbs on the edge of the forest. Sometimes the tree can be climbed or felled. Or leaves, flowers, and fruits fallen on the ground beneath can be found.
In obtaining specimens, tools such as knives, machetes, and axes are indispensable. Also, pruning shears and a pruning hook or pole may be used.
A notebook with pencil or pen, a hand lens, and a ruler or measuring tape are useful. So are field glasses and a camera. It is important to carry the specimens from the forest to the office or base without losing parts, without damage, and without drying. Probably the best method is to carry a light press with old newspapers directly to the forest. Or the specimens can be placed in a canvas bag or wrapped in newspapers. Also, there are the large cans that are used with moist newspapers inside. For large fruits and seeds, paper sacks are useful.
Botanical specimens in the herbarium are dried and pressed, in order to preserve them better and save space. The challenge in drying the specimens is to remove the moisture with pressure, and rapidly. If it is not pressed, the specimen does not stay flat but wrinkles and folds. Then it is fragile and breaks or becomes damaged easily. If it is not dried rapidly and completely, mold damages it. Also, when dried rapidly the specimens retain their natural color better and do not lose leaves or other parts.
In an emergency, specimens can be pressed with only some newspapers and a weight, such as books, boards, bricks, or stones.
Generally a wood press, size 12 by 17 or 18 inches, with two straps of leather or canvas is used.
The old newspapers or newsprint that are folded for the specimens should be the same size as the press. Also, 50 to 100 or more sheets of blotting paper or driers such as felt are needed.
The sample is arranged within the newspaper. It should not be larger than the cardboard mounting sheets, which measure 16-1/2 by 11-1/2 inches. A large specimen can be folded in the form of V, N, or M. Since the mounting sheet and pressed specimen have only two dimensions instead of three, some leaves and twigs should be removed, leaving the base of the petioles to indicate the leaf arrangement. Generally one should not arrange a leaf directly on top of another. If too many leaves are left, the specimen does not dry well and the leaves underneath cannot be seen.
Outside, on the corner of the newspaper sheet, can be placed the number of the specimen that corresponds to the number of the collector in his notebook. Between each two folded papers containing specimens is inserted a drier. When all the specimens are arranged in papers, the press is tightened and fastened.
The press should be put in a warm dry place. Daily, or twice daily, the driers are changed until the specimens within the papers become completely dry and break when they are bent. The first time that the driers are changed the specimens should be examined and rearranged as needed; those that have become folded should be straightened. The moist driers are dried in the sun, near a stove, or placed one by one against the walls and on the floor of a room. If driers are lacking, newspapers can be utilized. The time for drying varies from a few days up to a week, depending upon the size of the specimens, thickness of the leaves, etc. This method is rather slow, consumes much time, and does not prepare good specimens of trees with thick leaves. However, it serves well enough for foresters who do not collect many specimens and do not wish to carry much equipment.
Botanists who collect botanical specimens in quantities in tropical regions always use heat to dry the specimens rapidly. In the laboratory, electric ovens with ventilators or fans, or an apparatus of electric heaters or electric lightbulbs, can be used under the press.
In the field, a portable stove of gasoline or kerosene or kerosene lanterns can be employed.
With heat, corrugated sheets or ventilators of cardboard or metal are needed in order that the hot air can pass within the press and remove the water from the specimens. The corrugated sheets have the same size as the press. Those of cardboard can be flat on one or both sides. The metal sheets are made of aluminum or iron and last longer. They fit together in less space and dry the specimens in half the time required with cardboard. After 12 hours or more in an ordinary press with driers, the corrugated sheets are inserted in place of every second drier, and the press is mounted above the stove. A cloth is placed around the stove and fastened tightly around the bottom of the press, but opened near the bottom or on one side to permit entrance of air. With metal sheets the majority of the specimens will dry within 12 to 24 hours. At about the middle of this time the straps should be tightened and the press turned over. As there is danger of fire, the stove never should be left unattended.
After being dried the specimens should be arranged in order by number and kept in cardboard boxes or packages in a dry place. If they are stored for much time, insecticides should be applied.
From time to time, foresters collect botanical specimens for large herbaria and also use the herbaria in identification. Perhaps with the duplicate specimens they may make small herbaria of the regions where they work. Therefore, they should know something of the arrangement and care of the herbarium. How to identify specimens in the herbarium was discussed earlier.
The mounting of specimens
After being identified and before being placed in the steel or wood cabinets, the specimens are mounted on mounting sheets of white cardboard. These cardboards, which measure 16-1/2 by 11-1/2 inches, should be of good, durable quality. In some herbaria the specimens are mounted with glue or paste. In others, narrow pieces of gummed cloth tape are used. With both methods the thick parts, such as stout twigs and large fruits, can be sewed with needle and thread. Loose parts, such as additional flowers and fruits, are placed in pockets or envelopes glued to the mounting sheet.
The label is glued or pasted on the lower right corner of the mounting sheet. Generally labels are printed in part. The notes by the collector should be added with a typewriter. In addition there are added the scientific name with author, the name of the person who made the identification, and preferably also the year of the identification.
The mounted specimens of a genus, or of a species if there are many, are placed in a folded cardboard sheet 12 by 17-1/4 inches after folding. The generic name is placed on the lower left corner outside.
Arrangement of the herbarium
Large herbaria generally follow a natural system of classification in their arrangement. The most popular is that of Dalla Torre and Harms, based upon that of Engler and Prantl (1887), with numbers for the families and genera. Each genus of seed plants has a number, and the specimens are arranged and may be found in this numerical order.
In a small herbarium of a region, or in a personal herbarium, it is simpler to follow the order of the botanical flora of the country. Generally the order of the families in botanical references is that of Engler and Prantl (1887). Within a family, it is simplest to arrange the genera and species alphabetically.
Protection against insects and mold
It is always necessary to protect the herbarium against insects and, in humid climates, also from mold. No method is perfect. Perhaps the simplest is to place repellents, such as paradichlorobenzene or naphthaline, in small cloth sacks or pockets within each cabinet, at the top. From time to time, every few months during the year, it is necessary to add more chemicals.
Mercuric chloride (bichloride of mercury) in solution is employed for killing insects on botanical specimens. Before mounting, the specimen is dipped into this solution and then dried. Fumigation with carbon disulfide or a poisonous gas is another method. Or the specimens can be placed in a special cabinet or in an oven, where insects may be killed with heat.
Engler and Prantl. 1887 and later. Die naturlichen pflanzenfamilien: The natural plant families. [place of publ. unknown]:[publisher unknown].
This article was adapted with the kind permission of the publisher from:
Little, E.L. 2002. "Notes on Tropical Dendrology." In: Vozzo, J.A. (Ed). Tropical Tree Seed Manual. USDA Agriculture Handbook 721. US Forest Service, Washington, DC.
An electronic version of the Tropical Tree Seed Manual can be downloaded from: http://www.rngr.net/Publications
About the author
Elbert L. Little, Jr. had a many decades-long career as a dendrologist with the U.S. Forest Service. His multifaceted career includes being a university professor, a forest ecologist, a forest botanist, a tropical dendrologist, and an author of tree books. Everyone significantly involved with forestry has been influenced by Little. His contributions are appreciated throughout the world. Little has written some 23 books, including more than 150 handbooks, bulletins, and articles. His work has covered trees from the Arctic of Alaska to the tropics of Central and South America and the Caribbean and Hawaiian islands. The books include a five-volume atlas series on trees of the United States. Many of Little's books are in English as well as Spanish, a language in which Little is fluent.