Vicki Funk and the Uses for a Herbarium

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Montanoa hibiscifolia, photo by Forest & Kim Starr.

Early in my romance with herbaria I came across an article by Vicki Funk called “100 Uses for an Herbarium (Well at Least 72).”  Learning about the many ways plant collections can be utilized got me even more excited about them.  I also felt I had met a friendly member of the herbarium community, someone with a sense of humor.  She came up with a great title for her piece and then stuck with it even though she didn’t quite get to the magic number her title promised.  In the piece, Funk lists herbarium functions from verifying plant Latin names in issues of nomenclature, to serving as a repository for voucher specimens, to making specimens available to students and interested members of the public.  This article was written in 2004, and I am sure that Funk could come up with many more roles today.  She in fact does move in that direction in a major review article she recently published on “Collections-Based Science in the 21st Century” (2018).  I plan to use that article as the basis for this series of posts, but first I’ll say a little more about Vicky Funk, who seems to me to be the epitome of a plant systematist in the 21st century.

Focusing on Funk’s work right now is particularly timely because she has won the 2018 Asa Gray Award, the American Society of Plant Taxonomists’ highest honor.  The fact that her nomination was accompanied by 18 letters of support suggests just how deserved this recognition is.  Funk is a research scientist and curator at the U.S. National Herbarium in the Department of Botany at the National Museum of Natural History, part of the Smithsonian Institution.  She is an expert on the Asteraceae or Compositae and is lead editor for the 2009 Compositae: Systematics, Evolution, and Biogeography of the Compositae.  This is a massive work in every sense of the term because it treats one of the largest flowering plant families.  She has also been involved in the creation of the digital Global Compositae Checklist.

Funk received her Ph.D. from Ohio State University for work on Montanoa, a genus of plants with daisy-like flowers in the Heliantheae or sunflower tribe of the Asteraceae.  They are native to Central and South America, but since then Funk has worked in Hawaii, Guyana, and a number of other places, and perhaps most importantly in the developing field of phylogenetics.  She has also been an important figure in the development of plant cladistics and is coauthor of the classic, The Compleat Cladist.  While doing all this research, she has been a good citizen of the plant systematics community as president of both the American Society of Plant Taxonomists and the International Association of Plant Taxonomists.  I have yet to meet Funk, in part because I am in awe of her.  However I have heard her speak; her passion, intelligence, and good sense come through along with her deep and comprehensive knowledge of the field.

Funk has also been a hard working member of the Smithsonian scientific community.  I keep up with her through the pages of the U.S. National Herbarium’s newsletter that has the great title The Plant Press and is available online.  The first issue I read was from 2007 when she had the lead article on the 20-year project of the National Museum of Natural History called the Biological Diversity of the Guiana Shield program.  As Funk describes it, the shield is a geological formation of igneous and metamorphic rock that underlies the northeast corner of South America and includes parts of Venezuela, Guyana, Surinam, French Guiana, Brazil, and Columbia.   At the point when she was writing, the Shield plants checklist, of which she was an editor, was in press.  It has proven to be an important resource since its publication in 2007.  I should note that her article includes a photo of herself and two colleagues doing what is stated to be their “best” imitation of a jacana, a South American marsh bird, standing on one leg.  In a later issue of The Plant Press, (April-June 2011), she is pictured more sedately with the University of the District of Columbia students she was mentoring.  In most photos Funk is wearing Hawaiian patterned shirts replete with large tropical blooms, seemingly to remind herself of her work on Hawaiian plants and to provide others with a pleasant aesthetic experience.

But while Funk can be light-hearted, she can also be deadly serious, as she was in the October 2014 issue of The Plant Press with the opening lead article:  “The Erosion of Collections-Based Science: Alarming Trend or Coincidence?”  She unfortunately sides with the first alternative, citing a number of disturbing cases over the prior years, including elimination of the science program at the Milwaukee Public Museum, dwindling support for scientific research at Fairchild Tropical Botanic Garden in Florida, closing of the science program at the Brooklyn Botanic Garden, and diminishment of programs and staff at the California Academy of Sciences, the Field Museum in Chicago, and the Royal Botanic Gardens, Kew.  Funk then goes on to outline the results of these cuts:  less projects in developing nations to assist in their scientific and economic development, weakening of education programs in the life sciences, and reduction in research on such crucial topics as climate change.  As the following posts will illustrate, these were hardly Funk’s last words on these topics.  She is in the forefront of the effort to support the future of systematics and environmental studies.

References

Funk, V. A., & International Association for Plant Taxonomy. (2009). Systematics, evolution, and biogeography of Compositae. Vienna, Austria: International Association for Plant Taxonomy, Institute of Botany, University of Vienna.

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Libraries and Botany: New York, New York

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Specimen of Diopyros virginiana collected from the site of the Elgin Botanic Garden in 1829, New York Botanical Garden Steere Herbarium

Since the joint CBHL/EBHL meeting (see earlier post) was held in New York, it’s not surprising that there were several presentations related to the metropolis.  It seems fitting to end this series of posts with a review of them.  After a welcome from Susan Fraser, director of NYBG’s Mertz Library, the first major speaker of the conference was Eric Sanderson of the Wildlife Conservation Society, headquartered across the street from the New York Botanical Garden, at the Bronx Zoo.  For many years Sanderson has had a leading role in research on what New York was like before Henry Hudson sailed into the mouth of the Hudson River in 1609.  The indigenous people called the large island he found Mannahatta, and that became the name for Sanderson’s endeavor and the title of the book he published in 2009.  Using mapping technology coupled with old maps, historical accounts of the area, specimens collected there in the past, and what is known about the ecology and geology of the island, Sanderson’s team identified 54 different ecosystem types on Mannahatta.  This is a large number for that sized piece of land, and the result of its extensive wetlands along with its varied geological features.  There were also an estimated 600 species of plants.

More recently Sanderson has led an effort to produce the same kind of modeling for New York City’s other four boroughs.  Called Welikia, it too has a website that is still under construction, but includes all the information from the Mannahatta Project.  These are not just interesting exercises in environmental history, they aim at helping the citizens of New York understand the biodiversity that once existed there and how to preserve and nurture as much of it as possible.  It is unlikely that bears will again roam Manhattan, but red-tailed hawks are flourishing (Winn, 1998), and I’ve seen a coyote ambling inside NYBG’s fence as I was stuck in traffic trying to get there.

On the second day of the conference, the botanical illustrator Bobbi Angell presented on the formidable botanical art collection housed at NYBG.  Angell has spent her life creating pen-and-ink drawings to illustrate the scientific work of the garden’s botanists, including many for the seven volume Intermountain Flora: Vascular Plants of the Intermountain West, USA.  The last volume was just recently published (2017) and includes not only some of Angell’s illustrations but biographies of her and other illustrators and botanists who worked on this project that was first envisioned by Bassett Maguire in the 1930s.  There will be more on the editors, Patricia Holmgren and Noel Holmgren, in a future post.

Angell didn’t dwell on her accomplishments, but instead discussed some of the other contributors to the 30,000 pieces in the NYBG art collection.  These include the great French botanical painter Pierre-Joseph Redouté with 10 paintings on linen, but Angell concentrated on 20th and 21st-century artists, including Alexandria Taylor and Frances Horne who did illustrations respectively for Elizabeth Britton and Nathaniel Lord Britton.  Both were distinguished botanists and Britton was NYBG’s founding director.  Angell spoke reverently of artists whom she knew including Anne Ophelia Todd Dowden, who left her finished works to the Hunt Institute for Botanical Documentation in Pittsburgh, and her working drawings to NYBG, an interesting division.  Then there was Rupert Barneby a self-taught botanist and artist who did research at the garden and became an expert on legumes.   He created his own illustrations until he injured his hand.  Angell ended with a plea for more of the botanical art in library collections to be made available online and a mention of the American Society of Botanical Artists, which has a wonderful journal for members as well as a website on which they can present their work.

The final presentation of the meeting was a public lecture by Victoria Johnson to celebrate the publication of her book, American Eden: David Hosack, Botany, and Medicine in the Garden of the Early Republic (2018).  She began the book and her talk very effectively by telling the story of how David Hosack, a physician, treated a New York boy dying of fever in 1797.  Hosack had tried everything he could without success, and so decided to lower the boy into warm bathwater with cinchona bark mixed in.  Several of these treatments led to the patient’s recovery and to a tearful thank you from his father.  Johnson then paused, and revealed that the father was Alexander Hamilton.  After this surprise, she went on describe some of what she writes about in her book:  how Hosack trained as a physician in the United States and Britain where he developed an interest in botany, even studying with James Edward Smith the founder of the Linnean Society; how he set up a medical practice in New York, obviously attracting an elite clientele; how he developed a plan to create a botanical garden in the city as a way to nurture, study, and teach about medicinally useful plants.  He used his own money to buy 20 acres of land in what is now midtown Manhattan, but was then over three miles north of the city.  He called it the Elgin Botanic Garden after the Scottish town where his family originated.  He built a wall around the property as well as greenhouses and then bought an impressive selection of plants.

Hosack had a long and successful life as a physician, but his story is definitely bittersweet.  He was the attending physician when his friend Alexander Hamilton was shot in the duel with Aaron Burr (it turns out they both were interested in gardening).  The garden, begun in 1801, was destroyed in the 1820s after it had been bought by New York State and then handed over to Columbia College (now Columbia University) for management.  It was neglected and eventually leased by Columbia as real estate prices in that part of Manhattan started to soar. Eventually, it became the site of Rockefeller Center.  However, to end on a happier note, there are a few Elgin Garden specimens in the NYBG herbarium including Diosyros virginiana (see above).

Note: I would like thank all those involved in the wonderful CBHL/EBHL meeting, particularly Susan Fraser, Kathy Crosby, Esther Jackson, and Samantha D’Acunto.  I am also grateful to the participants from whom I learned so much, to Pat Jonas who nudged me to attend, and to Amy Kasameyer who introduced me to CBHL.

References

Holmgren, N. H., & Holmgren, P. K. (2017). Intermountain Flora: Vascular Plants of the Intermountain West, U.S.A (Vol. 7). New York, NY: New York Botanical Garden.

Johnson, V. (2018). American Eden: David Hosack, Botany, and Medicine in the Garden of the Early Republic. New York, NY: Norton.

Sanderson, E. W. (2009). Mannahatta: A Natural History of New York City. New York: Abrams.

Winn, M. (1998). Red-Tails in Love: A Wildlife Drama in Central Park. New York: Pantheon.

Books Old and New, Part 3: Irish Natural History

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McGill-Queen’s University Press, Montreal, Canada (1997)

This series of blog posts (1, 2) is called “Books Old and New” because I’m covering some that I read years ago and others that are recent publications.  A book that was published 20 years ago, but is new to me is Nature in Ireland (Foster, 1997), a collection of essays that runs the gamut from geological history to present-day issues in forest conservation.  There is botany here, but I didn’t read this book primarily for that, but rather because I am attempting to finally get to know my parent’s native land from the biological perspective.  I’ve been steeped in its culture and history from birth, and since my mother did win a school prize in botany, I learned something of its plant life.  However, this mostly amounted to her complaining about plants that grew well in Ireland, such as primroses, but had to be coaxed in hotter and drier New York.

My mother learned in school that the Irish terrain resembled a soup bowl in that most of the mountains were along the coast with flat plains in the center.  Nothing is that simple, of course, but the first essay, “The Testimony of the Rocks” by John Feehan explains why this is so.  Feehan does a good job of illustrating how the Irish landscape came to be, and why the land in many areas is so rugged and filled with limestone.  His work is a good reminder that in order to understand plants, it’s necessary to understand the substrate on which they grow.  The most intriguing thing I learned here is that oldest known land plant, Cooksonia, can be found in Silurian fossils (428 Ma) from Devil’s Bit Mountain, a name I remember because my grandmother came from near there, and my mother explained that the gap in the mountain was said to be caused by the devil taking a bite out of it.

Several chapters deal with the history of Irish nature study, noting that the first written accounts date from a St. Augustin (not the St. Augustine) in the 8th century, a work studied by the biologist/polymath D’Arcy Thompson.  The next such treatment was by a visitor named Giraldus in the 12th century; some of the information there may have come from natives.  The first report of Irish plants to go into print appears to be that of Richard Heaton, a British cleric posted to Ireland in 1630.  By this time the country was well under Britain’s thumb, so much of the work that follows was done by Anglo-Irish or British botanists.  Arthur Rowdon was a prominent landowner with one of the first greenhouses in Ireland.  He is important to botany because he was a friend of the botanical collector Hans Sloane through whom the British botanist William Sherard came to live at Rowdon’s estate, perhaps as a tutor for his sons.  Sherard studied Irish plants and eventually became professor of botany at Oxford.  He was a friend of another Irishman, Thomas Molyneux, who acquired a herbarium created by the 17th-century pharmacist Antoni Gaymans.  This collection was annotated by Sherard and is still extant (Heniger & Sosef, 1989).  These are the kinds interesting side paths that run through the book.

Another one involves Caleb Threlkeld, who wrote the first Irish flora in 1727.  There is evidence that he must have seen a copy of Heaton’s work, and some of his text is derivative, using material from John Ray’s treatment of Irish plants.  However, Threlkeld made a real contribution of his own by noting when and where he saw the plants he described.  Also, present-day Irish botanists have studied old specimens at the Trinity College, Dublin herbarium and make a case that these were collected by Threlkeld, thus substantiating his observations (Doogue & Parnell, 1992).  The Trinity herbarium was also home base for the algologist William Henry Harvey, who added substantially to its collection with specimens from South Africa and Australia, including his reference herbarium from his visit to the latter.

When I met the Trinity herbarium’s present keeper, John Parnell, he emphasized that Harvey did many of his own illustrations, even to the point of making the engravings, because he wanted to insure the accuracy of what went into print.  Harvey’s work is magnificent, but it is not among the few botanical illustrations reproduced in the book, which is generally short on images.  There is, however, a chapter on “The Art of Nature Illustration” by Martyn Anglesea that cites several noted Irish artists, and highlights two who worked at another Dublin herbarium, that of the National Botanic Gardens of Ireland.  I have seen some of the work of Lydia Shackelton and Alice Jacob at the garden and it is amazing, especially the watercolors they did of orchids for Frederick Moore—a herbarium curator and expert on the family.

Before leaving this book, I have to mention Robert Lloyd Praeger who wrote The Way I Went, what some consider the best book for the general reader on the natural history and topography of Ireland.  He is most noted for his leadership of the Clare Island Survey (1909-1915), which involved over 100 amateurs and professionals and resulted in a landmark publication that set the bar high for future such European studies (Jones & Steer, 2009).  The Royal Irish Academy added to its value by funding a new survey of the island to mark the hundredth anniversary of the first.

References

Doogue, D., & Parnell, J. (1992). Fragments of an eighteenth century herbarium, possibly that of Caleb Threlkeld, in Trinity College, Dublin (TCD). Glasra, 1(2), 99–109.

Foster, J. W. (Ed.). (1997). Nature in Ireland. Montreal, Canada: McGill-Queen’s University Press.

Heniger, J., & Sosef, M. S. M. (1989). Antoni Gaymans (ca 1630–1680) and his herbaria. Archives of Natural History, 16(2), 147–168.

Jones, R., & Steer, M. (2009). Darwin, Praeger and the Clare Island Surveys. Dublin: Royal Irish Academy.

Praeger, R. Ll. (1937). The Way That I Went. Dublin, Ireland: Hodges, Figgis.

Threlkeld, C. (1727). Synopsis stirpium Hibernicarum alphabeticæ dispositarum. Dublin, Ireland: Powell.

The Algal World: Diatoms

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Diatom plate from Haeckel’s Art Forms in Nature

I was first attracted to diatoms by their exquisite beauty. When I studied aesthetics many years ago, beauty was often defined in terms of categories such as symmetry and form, and diatoms are definitely exemplars of both. They are one-celled algae, each encased in a glassy silica shell that varies with species. These structures can be elongated, triangular, circular, square, or more elaborately shaped. There is no better introduction to them than the diatom plate [shown above] from Ernst Haeckel’s Art Forms in Nature (1904). There are also great microscope photographs of diatoms on the web, at sites such as Micropolitan University. If you want more than just images, the Natural History Museum, London has Diatoms Online and the Academy of Natural Sciences (ANS) in Philadelphia (now part of Drexel University) has a Diatom Herbarium, both a real and a virtual space.

I visited the diatom collection at ANS two years ago and was drawn into a very different kind of herbarium world. Yes, there are metal cabinets, but they are filled with boxes of microscope slides, not sheets of white paper in folders. This collection was begun in the mid-19th century by members of the ANS who were interested in microscopy. At the time, this was, like seaweed, a hobby for many people who had the money to have leisure time and to buy a microscope. Some were physicians who had some familiarity with microscopes through their profession; others included bankers and industrialists who simply became fascinated with what couldn’t be seen with the naked eye. Like seaweed collecting, this was an area of interest in Britain, and also on the Continent, and had begun in the 17th century (Stafford, 1996). By the mid-19th century, microscope optics had improved and the instruments were easier to use. Many of the ANS microscopists were interested in fossilized diatoms found in diatomaceous earth, which could be found in areas around Philadelphia. This fine, sandy material is used in polishing among other things and represents the remains of organisms that lived in great numbers millions of years ago. Since diatoms are responsible for 20-25% of the earth’s carbon fixation, it’s difficult to overestimate their abundance, both now and in the past.

Eventually, the microscopists’ diatom collections morphed into the ANS Diatom Herbarium, which now houses the second largest such assemblage in the world. Along with slides, there are small glass bottles filled with diatomaceous earth collected in various locations. These are particularly difficult to catalog because each sample contains many species. In some cases, small portions of these sands have been separated out with individual species mounted on slides, but as Maria Popanova, the curator of the collection, notes the bottle that was the source of a particular mount wasn’t always recorded on the slide. There are ways of backtracking using dates and collection sites, but it’s time-consuming work and slows down digitization of the collection. However, 63,000 specimens are now available online. Also at ANS are rare 19th-century exsiccatae that contain many type specimens. These are store in book-like boxes with specimens either mounted on slides or in tiny envelopes. A counterpoint to these historically important items are posters on the walls of scanning electron microscope images of diatoms revealing an even more elaborate detail than that provided by a light microscope. The images are more expensive to produce so not every diatom receives this attention, but these images highlight the complexity of these minute structures.

I could easily dwell on the aesthetic aspects of these creatures, but I want to also stress their scientific significance. There are good reasons why the herbaria such as the ANS and NHS, among many others, maintain diatom collections. The cells can tell us a great deal about aquatic life of the past, the present, and the future. Diatoms serve as useful markers of aquatic ecosystem health. Their shells remain after death, providing stable evidence of water quality. A water sample’s use in monitoring usually deteriorates with time as organisms die, but this is a lesser problem with diatoms. Also, they are ubiquitous, found all over the world in both fresh and salt water. The species present at a site depend upon the presence or absence of pollution, among other factors.

Part of the research done at ANS involves water monitoring studies and having a rich diatom collection, including many type specimens, as reference adds weight to the findings. This work has a long history at the ANS, and the person most responsible for building its stature was Ruth Patrick (1907-2013). She had a doctorate based on diatom research from the University of Virginia and wanted to volunteer at the ANS in the 1930s. She was kept out for several years because they didn’t accept women. She finally became a volunteer in 1935, serving first as a virtual servant to the Microscopy Section, setting out specimens for their meetings among other duties. She eventually became the first woman member of the ANS. In the late 1940s, after she became a paid employee, Patrick founded the ANS Limnology Department. Through her work, the ANS developed a focus on freshwater diatoms; before that it had collected mostly fossils and saltwater species. She directed studies on rivers and streams, especially in terms of using diatoms to gauge water quality, and her influence lives on in the ANS’s Patrick Center for Environmental Research.

References

Haeckel, E. (1904). Art Forms in Nature (Vol. 1974 ed.). New York: Dover.

Stafford, B. M. (1996). Artful Science: Enlightenment Entertainment and the Eclipse of Visual Education. Cambridge, MA: The MIT Press.

Uses of Herbaria: Biogeography and Climate Change

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iDigBio is an NSF-funded program to digitize US natural history collections

Alexander von Humboldt (1759-1769) is often considered the father of biogeography because of his crucial work on this subject in South America, and his writings and diagrams showing the link between terrain and vegetation (Humboldt & Bonpland, 2009). However, even during the Renaissance it was becoming obvious that terrain and climate greatly influence plant life. Many of the plants of northern Europe turned out to be different from the Mediterranean plants described by ancient authors including Theophrastus and Dioscorides. Place mattered and as botanists went on field trips and collected specimens, they become more aware of local differences in plant habitats. Now plant distribution is a major focus for botanists and ecologists, and herbaria are important in documenting what grows where. Species distribution maps are a staple of floras.

Today, with the combination of GPS coordinate mapping and digitization of specimen data, it’s possible to generate distribution maps relatively easily from online herbarium data. However, there is a question as to how accurate these maps are. As with any output, the answer depends upon the input: the accuracy of the localities. There is software such as GEOLocate and the MaNIS Calculator that will generate the probability of a plant being within a particular radius. Doing georeferencing well is time-consuming, and there are millions of sheets requiring attention. Even if all the data were optimal, there is the question of what percentage of the sheets are available online? If the species distribution maps are based on online data, and that only represents, say, a quarter of the specimens, then how accurate is it? In addition, there is collection bias. In other words, rarely are regions sampled uniformly. Studies show that areas accessible via roads, rivers or railroads are more likely to be thoroughly canvased than are more remote locales, so all the error can’t be blamed on computers (Vetter, 2016). Some of the best studies are those that combine herbarium data with direct observation in an area (Martin et al., 2014; Mohandass & Campbell, 2015).

At the present there can’t be any discussion of biogeography without bringing up climate change. At the moment, interest in this topic is driving not only research on herbarium collections but also their digitization. Herbaria are among the few places where there are records that range over more than 100 years, in some cases 200-400 years, and they become more valuable by the day. Records can be studied in a variety of ways to glean information on climate and habitat characteristics in the past. The area that has been developed most substantially is phenology, the study of natural events that can be pinpointed in time. For plants this is often budding, flowering, or seed setting. Though this has not always been true in the past, it is now standard herbarium practice to collect specimens that are in flower or have seeds or fruit. Since collection data are always recorded for specimens, researchers can track flowering or fruiting over the years to detect differences that might be related to climate change. Again, if digitized and imaged specimens are used, the study is limited by the richness of the sample, but it does make for more efficient investigation. There have been several studies validating the methods used in this research (Davis et al., 2015; Spellman et al., 2016). To date, changes in flowering times have been noted in orchids (Molnar et al., 2012), eucalypts (Rawal et al., 2014), and perennial herbs (Matthews & Mazer, 2015) among others; changes were also recorded in leaf-out times for trees (Everill et al., 2014; Zohner & Renner, 2014). With projects like NSF’s iDigBio, which has resulted in a portal with access to over 75 million natural history specimens, the problems of small sample sizes are dwindling, but still significant.

Still other ways to document climate change with specimens include counting the stomata on leaves. This is obviously more time-consuming, but the number of studies in this area suggest that it’s considered a fertile area of investigation. Stomata are the pores in a leaf through which plants absorb CO2, the fuel for photosynthesis. Since global warming is precipitated by the increase in atmospheric CO2 due to fossil fuel combustion, it’s not surprising that in several species, there has been a decrease in stomatal density. Plants just don’t need as many pores to absorb the same amount of CO2. In addition, leaves can give evidence of other types of environmental change. An alteration in leaf area over the past three centuries has been noted for some species (Peñuelas & Matamala, 1990). Also, there was a marked decrease in leaf sulfur levels in the years after the clean air act was passed and an increase in nitrogen with increased use of fertilizers (Peñuelas & Filella, 2001). Someone has even studied the distance over time between leaf teeth in the mulberry Hedycarya angustifolia over the past 160 years to see if an increase in temperature had affected this trait. However, despite the painstaking analysis, researchers couldn’t find any significant change (Scarr & Cocking, 2014). This work shows how many ways climate change can affect plants, and how clever botanists and ecologists employ varied plant characteristics in collecting data on this phenomenon. Having different types of data strengthens the case for the significant impact of climate on plant growth and also on the survival of species. I’ll present more evidence for this in the next post.

References

Davis, C. C., Willis, C. G., Connolly, B., Kelly, C., & Ellison, A. M. (2015). Herbarium records are reliable sources of phenological change driven by climate and provide novel insights into species’ phenological cueing mechanisms. American Journal of Botany, 102(10), 1599–1609.

Everill, P. H., Primack, R. B., Ellwood, E. R., & Melaas, E. K. (2014). Determining past leaf-out times of New England’s deciduous forests from herbarium specimens. American Journal of Botany, 101(8), 1293–1300.

Humboldt, A. von, & Bonpland, A. (2009). Essay on the Geography of Plants. (S. T. Jackson, Ed., S. Romanowski, Trans.). Chicago, IL: University of Chicago Press.

Martin, M. D., Zimmer, E. A., Olsen, M. T., Foote, A. D., Gilbert, M. T. P., & Brush, G. S. (2014). Herbarium specimens reveal a historical shift in phylogeographic structure of common ragweed during native range disturbance. Molecular Ecology, 23(7), 1701-1716.

Matthews, E. R., & Mazer, S. J. (2015). Historical changes in flowering phenology are governed by temperature × precipitation interactions in a widespread perennial herb in western North America. The New Phytologist, 210(1), 157-167.

Mohandass, D., & Campbell, M. J. (2015). Assessment of Roscoea population size in the Central Himalayas based on historical herbarium records and direct observation for the period 1913-2011. Journal of Biological Records, 0022015, 10–16.

Molnár, A., Tökölyi, J., Végvári, Z., Sramkó, G., Sulyok, J., Barta, Z., & Bronstein, J. (2012). Pollination mode predicts phenological response to climate change in terrestrial orchids: A case study from central Europe. Journal of Ecology, 100(5), 1141–1152.

Peñuelas, J., & Filella, I. (2001). Herbaria century record of increasing eutrophication in Spanish terrestrial ecosystems. Global Change Biology, 7(4), 427–433.

Peñuelas, J., & Matamala, R. (1990). Changes in N and S leaf content, stomatal density and specific leaf area of 14 plant species during the last three centuries of CO2 increase. Journal of Experimental Botany, 41(9), 1119–1124.

Rawal, D. S., Kasel, S., Keatley, M. R., & Nitschke, C. R. (2014). Herbarium records identify sensitivity of flowering phenology of eucalypts to climate: Implications for species response to climate change. Austral Ecology, 40(2), 117-125.

Scarr, M. J., & Cocking, J. (2014). Historical responses of distance between leaf teeth in the cool temperate rainforest tree Austral Mulberry “Hedycarya angustifolia” A. Cunn. from Victorian herbarium specimens. Victorian Naturalist, 131(2), 36–39.

Spellman, K. V., & Mulder, C. P. H. (2016). Validating herbarium-based phenology models using citizen-science data. BioScience, 66(10), 897–906.

Vetter, J. (2016). Field Life: Science in the American West during the Railroad Era. Pittsburgh, PA: University of Pittsburgh Press.

Zohner, C. M., & Renner, S. S. (2014). Common garden comparison of the leaf-out phenology of woody species from different native climates, combined with herbarium records, forecasts long-term change. Ecology Letters, 17(8), 1016-1025.