Are Herbaria Still Relevant in the 21st Century?

By Walter Fertig, Arizona State University herbarium

Originally published in Sego Lily 2016 Vol 39(1):6-8.

The oldest herbaria date to the Middle Ages when European physicians first learned that dried and pressed plants could retain their color and appearance for decades if properly preserved.  Initially specimens were bound in books to provide doctors with a handy reference for identifying the sources of herbal medicines.  Over time it became more convenient to keep specimens on loose sheets that could be arranged in various ways.  Nascent taxonomists could even begin to organize their collections according to patterns.  Linnaeus, the creator of our modern taxonomic system, had a home herbarium that he could rearrange as he saw fit, and other scholars kept personal collections too.  Ultimately, small collections coalesced into larger public repositories, often housed in major universities or botanical gardens.  In the 19th and early to mid 20th centuries, herbaria were at the forefront of research into the genealogical relationships of plants based on outward appearance (morphology) and internal anatomy.

Such work continues to this day, but has long been overshadowed by more sophisticated techniques and more modern analytical tools.  Not surprisingly, traditional herbarium taxonomy has declined in prestige and funding.  In the past twenty years one herbarium in seven has closed due to budget cuts or shifts in academic priorities (Deng 2015).  In most cases, these collections have been absorbed by larger institutions, such as the recent merger of the University of Missouri Herbarium by the Missouri Botanical Garden.  More ominous is the growing trend of vacant positions not being refilled, degree programs in botany disappearing, and reduced hours of operation.  Just this March, a major National Science Foundation program that has traditionally funded specimen digitization and large capital expenses (such as new cabinets) was suspended.

If herbaria are to survive, those of us who care about them need to do a better job of demonstrating their value to society.  While conventional taxonomic research remains important, herbaria are also increasingly relevant in the fields of ecology, biogeography, and conservation biology.  Specimens are also valuable for building public appreciation of plants and of botany in general.  Rather than hiding our specimens behind cabinet doors, we need to make them more accessible, especially digitally.

Each herbarium sheet has three main pieces of information.  The most obvious is the physical specimen itself: stems, leaves, roots, flowers, and fruits.  From these, researchers can determine the identity of the species and recognize the diversity among individual plants within and between populations.  Measurements and observations of specimens is the basis for species descriptions and identification keys.  Additional information can be gleaned from the internal chemistry of the specimens, especially genetic data from nuclear and organelle DNA. Such data can be used to reconstruct phylogenetic relationships among species, genera, and families.  Perhaps the most useful information, however, comes from the specimen label which records the name of the species (and any subsequent changes or corrections), the collector, the date of the collection, locality, and other data on habitat, elevation, associated species, or abundance.  These three datasets are the foundation of taxonomic research and can be especially useful in studies of ecology and conservation biology.

For taxonomists, the most important specimens are the type collections, which provide the basis for species names and taxonomic concepts.   When a new species is discovered, a holotype is designated and deposited in an herbarium to serve as the standard (or archetype) for which all other individuals of the species are compared.  A recent study found that nearly one-quarter of all newly documented species were already found within existing herbarium collections but had been initially misidentified or unidentified (Bebber et al. 2010).  The authors even suggested that as many as 70,000 undescribed plant species might still be lurking within the world’s herbaria. 

Herbarium specimens can also be a source for new records of pathogens and parasites.  In the 1990s, the late John Baxter, a retired mycologist, discovered over 30 state records of rust and smut fungi growing on plant specimens in the Rocky Mountain Herbarium at the University of Wyoming.  One of these was Puccinia yosemitana, a rust from California and Colorado that was new to Wyoming.  Baxter found it growing on a specimen  of Opal phlox (Phlox opalensis) that I had collected in SW Wyoming a few years earlier.  I had failed to notice the yellow-orange fruiting structures when making the voucher as part of a rare plant survey.

Specimen vouchers (deposited in herbaria) are important for documenting new occurrences of rare and unusual plants.  Compared to observation records or photographs, physical specimens are easier to corroborate if there is any debate about a report’s authenticity.  This can be especially important in ecological studies or when developing checklists for protected areas, such as national parks or wildlife refuges.

In the past, users of specimen data had to either visit herbaria in person or arrange to borrow material.  With the advent of digital databases, herbarium records are now readily available around the clock and from any home, office, or mobile device that has internet access (even in the field). On- line databases include standard label information (species name, collector, date, locality, habitat) and often have maps of collection sites and digital images of the actual specimen.  These data can be queried in numerous ways to create local or rangewide distribution maps or customized species lists.  Individual herbaria are increasingly pooling their digital data into regional and national networks, such as SEINet (Southwest Environmental Information Network), the Consortium of Intermountain Herbaria, or the Consortium of Pacific Northwest Herbaria, allowing users to access millions of records with ease.  Other digital products, such as interactive keys, image libraries, and links to original botanical literature, are greatly increasing the utility and scope of herbarium information.  

Brick-and-mortar herbaria (and the professional staff needed to maintain them) are still vital for plant identification services.  Potential clients range from farmers and ranchers, government biologists, and industry consultants to home gardeners, amateur naturalists, and school children: essentially anyone who might need assistance identifying mystery plants. Sometimes herbarium staff are asked to provide expertise on plant fragments rather than whole specimens.  Such “forensic botany” can help archeologists interpret prehistoric sites, paleoecologists infer past climates, and law enforcement officers solve crimes.

Herbaria can also be thought of as vast genetic libraries.  Rather than having to travel around the world to gather samples, researchers have millions of collections at their disposal, already identified to species and with collection dates and localities provided.  In the case of extinct or protected species, herbarium specimens may be the only material available for study.  Older specimens can offer a window into changes in genetic structure in populations and evidence of ongoing evolution.

There have been challenges in utilizing herbarium collections in molecular research.  Initially researchers had difficulty extracting sufficient quantities of DNA from old collections.  DNA can also be altered if specimens were pickled or dried improperly.  Some species are reluctant to give up their genetic resources, especially succulents or plants rich in sap or resins.

Recent advances in molecular techniques are resolving many of these problems. A recent study (Choi et al. 2015) found no relationship between the age of a specimen and the purity of DNA that could be extracted and later amplified.  Ames and Spooner (2008) used DNA from 200-year old herbarium specimens of Irish potato in Europe to match unique genetic markers with their source populations in the Andes and lowlands of Chile and help determine the multiple points of origin of this important crop plant.

Herbarium specimens can also be time capsules of past environmental conditions.  Atmospheric carbon dioxide levels have been recorded in herbarium specimens collected in the late 1700s and compared with recently collected  plants to document changes in the concentration of greenhouse gases since the industrial revolution (Bonal  et al. 2011).  Lichens are particularly useful bioindicators of air pollution and historical collections from herbaria have been used by researchers to trace the decrease in air quality and subsequent changes in the lichen flora in the Los Angeles area over the past century (Riddell et al. 2011).

Locality data from herbarium specimens is also useful in studying the spread of invasive weeds.  One example is Stinknet (Oncosiphon piluliferum), a malodorous annual weed from South Africa that recently became established in the American Southwest.  Based on herbarium collections, this species was first collected in Los Angeles and Phoenix in 1981.  It remained uncommon and infrequently documented until about 2005, when populations began to appear regularly in southern California and central Arizona.  At first the invader was a mystery, but again herbaria demonstrated their worth by providing weed specialists with the correct identification.  Information from collections is marking the steady progress of this species as it marches south towards Mexico.

Digital locality data from herbarium specimens can be used in modeling the potential distribution of weeds, rare plants, and other species of high management interest.  At the University of Wyoming, I used more than 325,000 digital records in the Rocky Mountain herbarium database to identify patterns in the presence and inferred absence of 100 randomly selected plant species with a mix of environmental variables (average monthly temperature and precipitation, bedrock geology, soil type, vegetation, etc.).  The resulting models identified areas of likely and unlikely habitat that could then be checked to determine if the target species was present.  This study resulted in the discovery of several new populations of critically endangered plant species.

Locality data from herbarium collections can also be used to identify gaps in the network of protected areas, such as national parks, wilderness areas, special botanical areas, and Nature Conservancy preserves.  In Wyoming, 10.6% of the state is “protected”, but these areas tend to be concentrated non-randomly in the northwest corner of the state and at high elevations.  Based on herbarium records, I found that 18% of the state’s plant species were completely absent from these protected areas.  Unprotected plants tended to be restricted to specific habitats and regions (such as deserts, grasslands, and the Black Hills) that were not well represented in the existing protected area network.  In addition, rare species were more than twice as likely to be unprotected as common species.  These results should be helpful in targeting specific areas and species in need of conservation attention (Fertig 2011).

Making herbaria relevant again

Hopefully the preceding examples have demonstrated the ongoing value of herbaria in contemporary research on plant taxonomy, ecology, and conservation biology.  Herbarium supporters need to share this message with the public, our academic colleagues, and those who control research funding.  I recommend the following actions:

1. Stop using images of scientists standing in front of open herbarium cabinets to illustrate our work (visit any herbarium home page and you will see what I am referring to).  Our focus needs to be on the contents of the cabinets and not the cabinets themselves! 
2. Expand the reach and quality of digital specimen databases and keep access to them free.
3. Provide technical services to the public, such as help with plant identifications, and do so with a smile. 
4. Support and participate in research across disciplines and at local, state, regional, and international scales (no working in isolation!)
5. Create a positive environment for students, colleagues, and visitors.
6. Hold more outreach events with the public.  Remember that people really like plants and are just as fascinated as we are by their diverse forms, colors, and beauty.  There is something about seeing (and holding) a plant in person, even if dried and pressed, that is far superior to a photograph or video.  Engaging visitors is a great way to recruit potential volunteers to mount, database, and file specimens and builds crucial support for the work that we do and love.

References

Ames, M. and D.M. Spooner.  2008.  DNA from herbarium specimens settles a controversy about origins of the European potato.  American Journal of Botany 95(2):252-257.

Bebber, D.P. et al. 2010. Herbaria are a major frontier for species discovery. PNAS 107(51):22169-22171.

Bonal, D.  Et al. 2011.  Leaf functional response to increasing atmospheric CO2 concentrations over the last century in two northern Amazonian tree species: a historical δ13C and δ18 O approach using herbarium samples.  Plant, Cell & Environment 34(8):1332-1344.

Choi, J., et al. 2015.  All that is gold does not glitter? Age, taxonomy, and ancient plant DNA quality.   PeerJ 3 e1087.

Deng, Boer. 2015.  Plant collections get pruned back.  Nature 523:16.

Fertig, W.F.  2011.  Strategies for plant conservation in Wyoming: Distributional modeling, gap analysis, and identifying species at risk.  Ph.D., Dept. of Botany, University of Wyoming.

Riddell, J. et al. 2011. Tracking lichen community composition changes due to declining air quality over the last century: the Nash legacy in southern California.  Bibliotheca Lichenologica 106:263-277.