Collecting Herbarium Specimens
From an appendix in Shinners & Mahler's Illustrated Flora of North Central Texas; copyright 1999 BRIT and Austin College
What Is An Herbarium?
A collection of pressed and dried plant specimens is known by botanists as an herbarium (plural herbaria). The word herbarium, as originally used, referred to a book about medicinal plants. Pitton de Tournefort (early French botanist and physician) around 1700 used the term for a collection of dried plants and his usage was taken up by Linnaeus (Arber 1938; Stearn 1957; Birdson & Forman 1992). Largely through Linnaeus's influence the word herbarium thus replaced such earlier terms as hortus siccus (dry garden) or hortus hyemalis (winter garden) (Arber 1938; Stearn 1957; Shinners 1958a). Luca Ghini (1490?--1556), a botany professor at the University of Bologna, Italy, is considered to have been the first person to dry plants under pressure, mount them on paper, and thus preserve them as a permanent record (Arber 1938; Birdson & Forman 1992). The usefulness of such specimens was soon apparent and his technique was disseminated over Europe by his pupils (Arber 1938). By the time of Carl Linnaeus (1707--1778), this method was well known and widely used (Stearn 1957). The oldest surviving herbarium is that of Ghini's pupil Gherardo Cibo, who began to collect plants at least as early as 1532 (Arber 1938). Other early herbaria were developed in various countries including England, France, Germany, and Switzerland and, in all, more than twenty 16th century collections survive in different European cities (Arber 1938; Valdés 1993). According to Stearn (1957), "The older herbaria consisted of specimens on sheets bound into [book-like] volumes. Linnaeus never adopted this inelastic and expensive procedure but mounted his specimens on loose sheets stored horizontally which could be easily re-arranged and to which other specimens could be added when necessary. Probably due to Linnaeus's example and teaching this method became general during the second half of the 18th century." Modern herbaria still utilize Linnaeus's basic system of mounting specimens individually on loose sheets. Today about 16,000 specimens that were at one time in Linnaeus's personal herbarium survive in England, Sweden, and France and can still be studied (Stearn 1957). From these beginnings, Holmgren et al. (1990) reported 2,639 herbaria world-wide with an estimated 272,800,926 specimens.
What Are Herbaria Used For?
Herbaria are among the most important tools in studying the plants of a given area, with the reasons for this importance being quite diverse (Benson 1979; Birdson & Forman 1992; Valdés 1993). Specific ways in which herbaria are used include: 1) Herbaria are invaluable reference collections used as means of identifying specimens of unknown plants. Even experienced botanists frequently need to refer to herbarium specimens in order to definitively identify a plant in question. In this way botanists are able to identify material for such organizations or individuals as poison centers, medical researchers, ranchers, law enforcement agencies, agricultural extension agents, or gardeners. 2) Herbarium specimens, which have an indefinite life if properly protected (the oldest in existence go back almost 500 years), also provide a valuable historical record of where plants occurred in the past in both space and time. A local example can be seen in Julien Reverchon's collections from the late 1800s and early 1900s made in the Dallas area. Because the natural vegetation of Dallas has been almost completely destroyed, without Reverchon's specimens we would have almost no knowledge of the previous richness of that flora. Also, herbarium specimens provide early documentation of the introduction of foreign weeds or the previous geographic limits of native plants (Shinners 1965). These examples demonstrate the importance of herbaria as a special type of museum and as such they are important storehouses of irreplaceable data. In a real sense, herbaria serve as ". . . a source of primary information about man's explorations and observations of the earth's vegetation. . . ." (Radford et al. 1974) and as ". . . the raw data underpinning our scientific knowledge of what kinds of plants exist, what their diagnostic features are, what range of variation exists within each, and where they occur" (B. Ertter, pers. comm.). To work with the actual specimens collected by Carl Linnaeus, Alexander von Humboldt, Asa Gray, or Charles Darwin not only provides us with valuable data, but also links us in a tangible way with the origins of modern science and our own disciplines. 3) Further, because many plants are available for only a small part of the year and because it is impossible to have live specimens of thousands of species from different regions readily available for study, herbaria provide the only practical way to have material of numerous species to compare and study---they thus are important research tools. Without a major herbarium such as BRIT (the official abbreviation of the herbarium of the Botanical Research Institute of Texas), a book such as this would have been impossible to produce. In addition, herbaria serve as a record or repository of the specimens upon which all taxonomic articles or books are usually based. In this way, other botanists can recheck and judge the validity of the work, critical steps in the scientific process. Also, because of the wealth of information contained in herbaria, they are essential research tools not only for taxonomists, but also for such diverse fields as ecology, endangered species research, entomology, environmental science, horticulture, medical botany, mycology, and palynology. 4) Finally, herbaria serve an important educational purpose. This ranges from their use by advanced undergraduates or graduate students learning taxonomic botany to grade school students learning about the importance of plants and the natural environment in their lives.
Collecting and Pressing Specimens
One of the most important considerations regarding plant collecting is to secure appropriate permission, whether on private or public land. This is critical in order to maintain a working relationship between landowners and botanists. It is particularly important to be sensitive to such landowner concerns as not damaging fences and properly closing gates. On public lands, such as parks and wildlife refuges, there are often strict collecting regulations with legal sanctions for not following these rules.
When selecting plants, collectors need to be sensitive to whether the plant to be collected is rare and whether the population will be adversely affected by having one or several individuals removed. Because populations of many native plants have been dramatically reduced by human activities, this concern is more important now that ever before. A rule of thumb sometimes given is the "1 to 20" rule---for every plant collected, there should be at least 20 others left in the population (Simpson 1997). Collectors should also bear in mind that certain plants (e.g., cacti, orchids) have special legal protection. Once it is ascertained that there is an adequate population for collecting, individuals representative of the range of variation in the population should be chosen. Individuals with herbivore or pathogen damage should not be ignored (Condon & Whalen 1983; McCain & Hennen 1986a, 1986b) and in fact should often be purposefully selected because such specimens are "information-rich" (J. Hennen, pers. comm.)---that is they often contain fungi, gall-inducing insects, or other pathogens and show characteristic plant responses to such organisms. Ideally, the entire plant, including roots or other underground structures, should be collected or, in the case of trees, shrubs, vines, or other large species, ample material representative of the plant should be obtained. Slender plants can be bent or folded to form a V, N, or even W shape on the sheet in order for them to fit (sometimes the point of the V can be stuck through a slit in the bottom of the newspaper to hold the plant in place). For tiny plants, it is appropriate to collect a number of individuals for each specimen needed. A general rule of thumb is that the folded half-sheet of newspaper being used in the pressing process (a full sheet torn in half) should be reasonably well covered by plant material without excessive overlap or crowding. The best specimens have both flowers and fruits---while this is often not possible, all specimens should have some reproductive structures (either spores, cones, flowers, or fruits). Because most taxonomic keys are based on reproductive characters, sterile specimens are often useless. In fact, many botanists collect extra flowers or fruits to use in identification. Seeds, fruits, or other parts that become easily detached and are in danger of being lost should be put in small envelopes or bags and kept with the specimen. Extremely large structures (e.g., pine cones, large fruits) cannot be pressed and have to be carefully numbered (to match the specimen from which they were detached) and stored separately. The highest quality specimens are probably obtained by carrying a lightweight press into the field and doing preliminary pressing there. Such a press is usually referred to as a "field press" and generally consists only of straps, lightweight end boards, two or three cardboards, and newspapers (Fig. 42). Because of the absence of blotters and most cardboards, a field press is much lighter than a regular press and is thus suitable for carrying some distance in the field. Specimens pressed in this way can later be rearranged (leaves flattened, etc.) before being put between blotters and cardboards for final pressing and drying. However, instead of using a field press, practicality sometimes dictates that plastic bags be used to transport the plants back to a car, kitchen table, laboratory, etc., for pressing. We have found that carrying a number of large zip-type bags (which can be reused) inside a plastic trash bag works well. Plants collected in this way and sprinkled with water can often be stored overnight in the plastic bag in a refrigerator with little loss of quality. In the past, botanists temporarily stored specimens in a metal container (called a vasculum) in folds of wet paper.
The pressing process begins by putting the plant in a single half-sheet of newspaper (22" [X]CHECK THESE 14") folded crosswise (the folded half-sheet of newspaper should thus measure 11" [X] 14"). While this size may seem arbitrary, all subsequent steps in the collecting/herbarium process are tied to this size---these include plant dryers, cardboards and blotters for drying, specially designed herbarium storage cases, certain size shipping boxes, etc. The leaves, flowers, and other structures should be arranged in as natural a manner as possible on the newspaper while at the same time trying to avoid excessive overlap. Folding or bending the plant is often necessary as is the trimming off of excess material. When trimming is done (e.g., excess leaves removed), it should be carried out in way that makes it clear that material was removed (e.g., a portion of the petiole of a removed leaf should be left). In order to insure the best possible results, delicate structures such as flowers can be given additional padding with small pieces of blotter or pads made of folded pieces of newspaper or paper towels. Another consideration is that leaves should be arranged so that both surfaces can be seen (hair characters of the lower surface are often important); likewise, all parts of the plant, especially reproductive structures, should be accessible for study. At least some flowers should be spread open so that the internal structures will be visible for examination. A number (corresponding to a number in a collecting notebook) is written on the lower corner of the half-sheet of newspaper on the left edge or bottom adjacent to the folds. Permanent, bold red felt-tip markers are very handy for marking newsprint. An absorbent felt or thick paper blotter is then placed on each side of the fold of newspaper containing the specimen and this "sandwich" is placed between two pieces of corrugated cardboard. Additional plants are treated in the same fashion until all have been put in the press. The result is the following sequence: cardboard, blotter, fold of newspaper with plant, blotter, cardboard, blotter, fold of newspaper with plant, etc. (Fig. 42). While it may at first seem a waste of space, specimens of only one species should be placed in each fold of newspaper---this prevents getting "mixed collections" that are often confusing. It is also necessary to treat each species separately because, as discussed below, it is important to accurately record detailed written information about each one. After the plant material has been placed in newspaper between blotters and cardboards, wooden (or other stiff material) end boards are put on each side of the entire stack and straps are used to apply pressure, thus "pressing" the plants (Fig. 42). In this manner, as the plants dry they do not shrivel and high quality specimens can be obtained. The blotters wick moisture away from the plants and the corrugations in the cardboards allow water to easily escape the press. Some botanists use only cardboards (no blotters), with little loss of specimen quality; this is frequently done when the weight of the press is an important consideration or when a source of blotters is not available. In order to speed the drying process (a necessity in humid areas such as many places in the tropics), a heat or forced air source is often necessary. An easy way to heat a press is to leave it in the back seat or trunk of a car. A roof rack is also an excellent place for a plant press. Plant dryers utilizing light bulbs as a heat source are easy and inexpensive to build and are usually used by professional botanists; however, care should be taken to avoid the danger of fire (Fig. 42). Thick materials (e.g., fruits, very thick stems, material of plants such as cacti) may be sliced in order to allow appropriate drying and to prevent unwieldy structures in the press.
Plants should stay in the press until they are dry. The time necessary is quite variable depending on whether a heat source or forced air source is used, the type of plant, the humidity of the ambient air, etc. If upon touching the plant any moisture can be sensed, it needs additional drying. Removing plants too quickly from the press will result in wrinkling or possibly molding. Likewise, leaving plants in a heated press for too long a period will cause damage (e.g., browning or fading of colors). A good rule of thumb is that most plants are dry after one or two days in a heated press while five to ten days is typical for plants in a press without any heat source. Be sure to tighten the press daily to prevent wrinkling. Also, without heat or forced air, it is often good to change blotters daily.
Making a Label
Just as important as the plant specimen itself is a properly done label. All data needed to make the label should be written down in a small notebook or "field book" at the time the plant is collected (e.g., Simpson 1997). Of crucial importance is accurate location data so that the site can be relocated by a stranger in the future. Most important are the state and county; also detailed location information such as landmarks, accurate distances, nearby towns or cities, adjacent streams, rivers, and lakes, or any other data to help relocate the site should be recorded. Other important information includes habitat (e.g., field, forest, weedy roadside, shallow water, soil type, whether the plant is growing in shade or sun), associated plants, collector, collection number, the date the plant was collected, and who was with the collector (these individuals could possibly help in the relocation of the site). The date should be given as 8 May 1996 because 08/05/96 usually means 5 August 1996 in the United States and 8 May 1996 in Europe. It is also very important to record information that will be not be obvious from the specimen (e.g., size or height of plant, in the case of trees diameter-at-breast-height---DBH, appearance of the bark, manner of growth---erect, climbing, prostrate, etc., were the flowers closed at a certain time of the day, pollinators observed, etc.) or that may be lost upon drying (flower color, odor, color of sap, presence of stinging hairs, sticky feel due to glandular hairs). Common names used locally or information on edibility or local uses are also valuable. Latitude and longitude and elevation are particularly valuable for researchers and should be recorded. These can be obtained from standard maps of most areas. However, recent technological advances have made getting such information much easier---inexpensive and accurate Global Positioning System (GPS) units are now readily available and give very accurate information. Specimens with such location data are especially valuable because they can be entered into databases with applications from the local to national levels---in Texas and elsewhere, major database projects are currently underway and GPS locations on specimens are highly recommended. Because all of the other information discussed above is recorded in the field notebook, only the collection number needs to be put on the fold of newspaper in the press. A unique number should be given to each collection that a botanist makes and these numbers should increase sequentially throughout his or her lifetime. Thus, if Lipscomb 3491 is a collection of Quercus alba, there will never be a different Lipscomb 3491. If two or more specimens of Quercus alba are collected at the same time and same place by the same collector (such specimens are termed "duplicates"), they are given the same number. Such "duplicates" are often distributed to several herbaria so that there is more than one record of a particular collection. Because herbarium specimens are in essence museum collections that need to last hundreds of years, the labels should be printed on acid-free paper with permanent ink. Do not use "white-out" or other correction techniques that will be lost over time. There is no standard label size, but in general a 4" [X] 4" label should accommodate all necessary information without taking up excessive space on the mounting paper the specimen will ultimately be attached to (such a size will also allow 4 labels to be made from a single 8 1/2" [X] 11" sheet of paper). The following are two examples of labels containing appropriate information:
Austin College Herbarium, Sherman, Texas
Plants of TEXAS
Cnidoscolus texanus (Müll.Arg.) Small Euphorbiaceae
GRAYSON County: Southwestern corner of county, ca. 4 km south of Tioga, just off (east of) Hwy 377, ca. 200 meters from southern edge of eastern arm of Lake Ray Roberts.
Open, sandy, weedy field with Cenchrus spinifex and Monarda punctata.
Plants herbaceous, ca. 1/2 to 1 m tall, common. Locally known as bull-nettle. Flowers white, sweet-scented; sap milky; foliage with glass-like hairs which break off in the skin and cause an intense burning sensation.
33º 26' 36.1" N 96º 55' 25.8" W (GPS)
Elevation: ca. 190 m 24 Sept. 1980
Coll.: Delzie Demaree with Robert Kral and Donna Ware No.: 65,967
Austin College Herbarium, Sherman, Texas
Cnidoscolus texanus (Müll.Arg.) Small Euphorbiaceae
Texas, Grayson Co., southwestern corner of county, ca. 4 km south of Tioga, just east of Hwy 377, ca. 200 meters from southern edge of eastern arm of Lake Ray Roberts in open, sandy, weedy field with Cenchrus spinifex and Monarda punctata.. Plants herbaceous, ca. 5--10 dm tall, common. Locally known as bull-nettle. Flowers white, sweet-scented; sap milky; foliage with glass-like hairs that break off in the skin and cause an intense burning sensation.
33º 26' 36.1" N 96º 55' 25.8" W (GPS); ca. 190 m.
24 Sep 1980
Delzie Demaree 65,967
with Robert Kral and Donna Ware
Putting Specimens in Permanent Collections
Once a specimen is dried and has an appropriate label, it can be studied or given to an herbarium for permanent storage and use in research and teaching. The proper method of donating specimens is to leave the specimen in the original half-sheet (fold) of newspaper in which it was pressed and insert the label; neither the specimen nor the label should be attached to the newspaper in any way---gluing, stapling, taping, or any other attachment method frequently damages the specimen and sometimes completely destroys its usefulness. Mounting the specimens and labels to museum quality paper for permanent storage and use in the herbarium is done by herbarium personnel properly trained in these techniques---for example, special attachment procedures and long-life glues are used. There are a number of major herbaria in Texas with the largest including those at the University of Texas in Austin, the Botanical Research Institute of Texas (BRIT) in Fort Worth, and Texas A&M University in College Station. Many other schools or organizations have valuable collections; of particular note in North Central Texas are the herbaria at Baylor University in Waco, Fort Worth Museum of Science and History, Fort Worth Nature Center, Howard Payne University in Brownwood, University of North Texas, and the University of Texas at Arlington. BRIT welcomes the donation of herbarium specimens and botanists there can be contacted at (817) 332-4441 or info@brit.org or Botanical Research Institute of Texas, 509 Pecan Street, Fort Worth, TX 76102-4060. Such specimens will be scientific contributions, will have permanent protection, and will be important resources for the future.
Getting Started Collecting Plants
How do you get started collecting plants? Unfortunately, pressing plants between the pages of books is usually not successful because the plants dry too slowly, loose their color, seldom dry flat, and tend to damage the book. Therefore one of the first steps is to make or buy a plant press (including two end boards, corrugated cardboards, blotters, and two straps). A simple press can be made by cutting two 12" [X] 18" pieces out of 3/8" or 1/2" plywood and then rounding the corners and sanding the surfaces to avoid injury from splinters. The 12" [X] 18" size is slightly larger that a folded half-sheet of newspaper and is thus ideal for making the correct size specimens. Other types of end boards can be made out of nearly any reasonably lightweight, sturdy material. Cardboards the same size as the press can be cut from boxes, paper towels can be substituted for blotters, and simple ropes at least 4 feet long can be used as straps. With such a simple system and proper care, excellent specimens can be made. Alternatively, ready-made, convenient presses can be purchased from the sources listed below. Probably the most important parts of the press are the straps---straps that can be easily tightened and thus ensure appropriate pressure increase both the quality of the specimens and the convenience of the process. We thus recommend that a pair of straps be purchased. Because herbaria are museums whose collections are intended to last hundreds of years, the other thing that needs to be purchased is acid-free paper for the labels; this can either be special archival paper or 100% cotton rag bond. Such quality paper will last indefinitely ensuring long-term use of the specimens. Appropriate paper can be obtained from the sources listed below or can often be purchased from or at least ordered through office supply stores. For reasons of clarity, if possible, labels should be typed on a typewriter or printed using a computer (as is now done by most botanists because of speed and practicality). A hand lens (10 power) is another extremely useful tool in working with and identifying plant specimens. Many plant parts are quite small including specialized hairs or scales and moderate magnification is often essential for accurate identification; hand lenses can also be purchased from the sources below.
Information for this appendix was obtained from Shinners (1958a), Smith (1971), Radford et al. (1974), Benson (1979), Birdson and Forman (1992), MacFarlane (1994), and Simpson (1997). More detailed information about plant collecting techniques can be gained from these sources. Birdson and Forman (1992) in their Herbarium Handbook, also provided an extensive treatment of herbarium techniques and management.