When it comes to discussing the uses for plant specimens, you can’t do better than refer to Vicki Funk’s classic 2004 article “100 Uses for an Herbarium (Well at Least 72).” It is thorough and succinct. So why am I bothering to write on the same topic, if Funk has covered it so brilliantly? Well, that would deprive me of the fun of exploring some of those uses in a little more detail and perhaps even unearthing one or two new ones. While service to botany may seem the obvious place to begin, I’m going to start with medicine, the field that prompted the creation of the first documented herbarium, that of the Italian botanist and professor of medical botany, Luca Ghini (1490-1556), founded the first botanical garden at Pisa. The garden was designed to introduce students to the plants that were used by apothecaries, so they would be able to recognize them. This was obviously the function of the herbarium as well, and several of Ghini’s students, including Andrea Cesalpino (1519-1603) and Ulisse Aldrovandi (1522-1605) created specimen collections that exist to this day. Apothecaries also took up the practice, with Hieronymus Harder (1523-1607) creating a dozen bound herbaria, eleven of which are still extant.
The link between herbaria and medicine continues to this day. Those doing research on herbal medicines are often required to create voucher specimens of the plants they are studying so others can verify the identification in the future (Eisenman et al., 2012). One problem in past research was the difficulty of getting consistent results from one batch of plant material to the next. Having some of the material itself preserved in a voucher makes it easier to check whether or not the same species, subspecies, or variety was used in both cases. Not only can the plants be visually examined, but chemical tests can be done on the material if necessary. Rainer Bussmann has a chapter on “Taxonomy—An Irreplaceable Tool for Validation of Herbal Medicine” if you would like to learn more on this topic.
Voucher herbarium specimens are required in almost all botanical research, because the plant itself is the best evidence for answering questions about what species was actually growing where at a particular time. The most valuable kind of voucher is the type specimen, the record of the plant that was used in describing the species for the first time. Since modern taxonomy dates back to the publication of names by Carl Linnaeus in Species Plantarum in 1753, it is no wonder that the material he studied is itself still being tracked down to give as full a record as possible of the plant specimens, and in some cases plant images, upon which he based his descriptions (Jarvis, 2007). To this day, journals such as Taxon require authors to list specimen numbers and the herbaria where they are located for all material studied in revising taxa.
With the advent of DNA sequencing, herbarium vouchers can now be used in an entirely new way. A small piece of a specimen may yield enough intact DNA for researchers to identify a species with DNA sequencing. There are a number of factors limiting success including age, method of preparation, and species, but there are now many papers documenting the reliability of the results. The rich information the studies can yield include improvement in the fungal phylogenetic tree (Dentinger et al., 2015), tentatively identifying plants on Linnaeus’s Hamerby’s estate as related to his type specimens (Andreasen et al., 2014), and employing herbarium specimens in large-scale genomics research.
There are also more conventional uses of specimens that are nonetheless critical to botany. The development of floras—lists of plants in a particular locale—are impossible without using herbaria for collecting information. And when botanists are looking for living specimens of a species, the logical place to begin is in the herbarium where they can discover the location of past collections for the plant in question. The Royal Botanic Gardens, Kew (Kew) produces seed collecting guides for botanists going to areas such as Mozambique. The guides include descriptions of each species with a photo of the herbarium sheet as well as of the live plant. Specimens also can be used to hunt for other things besides plants, like diamonds and gold. The palm-like plant, Pandanus candelabrum is rare because it only grows in soils containing kimberlite which is rich in magnesium, potassium, and phosphorus. Kimberlite is also the volcanic rock where diamonds are found. So P. candelabrum, which grows in Liberia, may make it a little easier to discover these gems. As for gold, particles of the metal in Eucalyptus specimens may indicate gold deposits in the area where the trees grew. Using this link to direct prospecting is still experimental. It is definitely a long way from panning for gold, but worth a try (Lintern et al., 2013). These are very specific examples of botanical biogeography, but this is a much broader topic that I’ll discuss in my next post.
Andreasen, K., Manktelow, M., Sehic, J., & Garkava-Gustavsson, L. (2014). Genetic identity of putative Linnaean plants: Successful DNA amplification of Linnaeus’s crab apple Malus baccata. Taxon, 63(2), 408–416.
Dentinger, B. T. M., Gaya, E., O’Brien, H., Suz, L. M., Lachlan, R., Díaz-Valderrama, J. R., … Aime, M. C. (2015). Tales from the crypt: genome mining from fungarium specimens improves resolution of the mushroom tree of life. Biological Journal of the Linnean Society, 117(1), 11-32.
Eisenman, S., Tucker, A., & Struwe, L. (2012). Voucher specimens are essential for documenting source material used in medicinal plant investigations. Journal of Medicinally Active Plants, 1(1), 30–43.
Jarvis, C. (2007). Order Out of Chaos: Linnaean Plant Names and Their Types. London, UK: Linnaean Society.
Lintern, M., Anand, R., Ryan, C., & Paterson, D. (2013). Natural gold particles in Eucalyptus leaves and their relevance to exploration for buried gold deposits. Nature Communications, 4, 2274.