Botany in the early years of the Arnold Arboretum required a good postman. Boxes of photographs and herbarium specimens passed back and forth on the railroad. Taxonomic questions would follow in letters, along with requests for more specimens (and usually more again). Charles Sprague Sargent, the founding director of the Arboretum, famously obsessed over the taxonomy of hawthorns (Crataegus). His work was comprehensive and exhaustive, leaving no leaf or flower unturned, and as such, his letters are filled with requests for specimens, fruits, and field descriptions of these small, confusing trees. Yet if hawthorns were first on Sargent’s mind, hickories (Carya), the prominent forest trees of eastern North America, were not far behind—often mentioned in the same burst of typewriter keystrokes.

Of course, Sargent travelled widely and frequently to study plants in the field—camping on mountainsides, riding in motorcars on dirt roads—but for a project like the Silva of North America, a fourteen-volume work on tree species native to the United States that was published between 1891 and 1902, Sargent needed assistants far and wide. The same was true for subsequent projects that aimed to disentangle specific taxonomic problems, like his synoptic treatment of North American hickories published in the Botanical Gazette in 1918. While Sargent worked on these projects—studying specimens and hand-written field descriptions at his desk on the third floor of the Arboretum’s administration building—it must have felt like reconstructing a crime scene from several states away, years after the fact, with only a team of freelance detectives who could occasionally be marshalled (when time and finances permitted) to search for evidence and knock on doors to interview witnesses.

Letter with hand-drawn illustration of tree root flare
Sepia photograph of tree
Sepia photograph of tree trunk

In a long and detailed letter to Thomas Grant Harbison, one of his most reliable field collectors in the southeast, Sargent professed immense confusion when it came to the hickories. “It begins to look as if all the characters on which we have been trying to base species are giving out,” he lamented in 1914, after providing several pages of notes on specimens Harbison had collected. “I think that … the same species may bear globose and oblong nuts, that the leaves may or may not be pubescent, and that the bark may vary enormously according to situation.”1

Evidence for solving these taxonomic mysteries could be frustratingly scant. Even if someone collected herbarium specimens in the middle of the growing season, Sargent would send them back to collect again in the fall. Specimens in hand often only confirmed that others were needed. When he received fruits from a hickory that Ernest Jesse Palmer had collected in Noel, Missouri, in 1915, Sargent told him it was “one of the most remarkable of all your Hickories,” yet the fruit had only wetted his desire to know more. “Will you tell me something about this tree, its size, place of growth, character of the bark, or anything else you may know about it? I have never seen any fruit like this.”2 Four years later, Palmer would send grafted material from the same tree—now considered a mockernut hickory (Carya tomentosa, accession 8014*A)—which still grows in the Arboretum’s hickory collection. Although spindly (much smaller than expected of a centenarian overstory species), the tree offers a robust reminder of the correspondence needed to conduct this kind of taxonomic inquiry.

Special Agents

Sargent’s crew of field correspondents began solidifying long before his interest in hickories. His first concerted research project was the Report on the Forests of North America (Exclusive of Mexico), an ambitious opening salvo launched as part of the 1880 United States Census, which aimed to describe and map the composition of forests across the country. Sargent logged significant miles to research the project himself—notably botanizing forests in Utah, California, and Oregon—but to complete such a wide-ranging project, he needed colleagues that ranged just as far. Several botanists were officially enlisted as “special agents” for the four-year project, but others became informal collaborators.3

Map from census showing density of hickory species in the eastern UnitedStates
Sargent’s Report on the Forests of North America (Exclusive of Mexico), published in 1884, included the first distribution maps for major North American tree genera, which were prepared by Andrew Robeson. Rather than presenting the distribution of individual Carya species on this map, the green shading suggests species richness—or the number of Carya species believed present at any particular site. The greatest density (eight species) was recorded in western Arkansas, the future location for significant collections by Sargent and his correspondents. Arnold Arboretum Archives

A number of the oldest hickories still growing at the Arboretum arrived due to the census project, including an exceptional specimen of pecan (Carya illinoinensis, accession 12913*A), tucked in the back corner of the hickory collection, where its straight trunk lofts the canopy nearly one hundred feet high. Fruit for this accession arrived from the ornithologist Robert Ridgway, the first full-time curator of birds at the United States National Museum, who had collected the material near Mount Carmel, Illinois, in 1882. Although Ridgway was based in Washington, DC, he continued to study the landscape of Illinois—his home state—while he prepared a two-volume treatise on the birds of the state.

Ridgway was an unofficial census correspondent. Yet his research on woodlands in southern Illinois (and adjacent portions of Indiana) was so rigorous—far surpassing the needs of the census—that Sargent encouraged him to publish his findings independently. The article ran forty pages in the Proceedings of the United States National Museum, published in 1882, the same year the Arboretum received seed shipments from Ridgway. In the report, Ridgway described the pecan as “one of the very largest trees of the forest” with a canopy that often “reared conspicuously above the surrounding tree-tops, even in a very lofty forest,” and he noted that one tree (unfortunately measured after it had been felled) had been documented with a canopy 175 feet (53 meters) high and a trunk diameter of 5 feet (1.5 meters).4 The pecan in the Arboretum collection, while not yet that size, suggests this pedigree.

Photograph of large shellbark hickory with men standing at base
An unattributed Garden and Forest editorial from 1889 suggested that hickories “are the despair of people who expect to be able to fit exactly every plant they encounter with the printed description of it in some book.” This supplementary illustration of a shellbark hickory (Carya laciniosa) was based on a Robert Ridgway photograph from southern Indiana. Arnold Arboretum Archives

A stand of nine shellbark hickories (Carya laciniosa, accessions 12898 and 20094) that grow in park-like planting atop Valley Road also arrived in 1882 from another census correspondent. George Washington Letterman had been enlisted as an official special agent to study the forests west of the lower Mississippi River, although the hickories were collected near his home in Allenton, Missouri, about thirty miles west of Saint Louis. Letterman was a school teacher and scheduled fieldwork around his classroom duties. In a humorous note to George Engelmann, a prominent botanist who was a physician and a close mentor to Sargent, Letterman alluded to this time constraint in April 1881. Because so many students had the measles that spring, he suggested he might cancel classes and gain an unexpected week for census fieldwork.

In the same note, Letterman also described the perplexities of hickories. “It seems that the hickory nuts puzzle every body, especially those who have not been able to see the trees in all stages of growth year after year,” he wrote, referring to an inquiry from the Illinois botanist George Vasey. “Don’t you think that something better than what the books now contain on the subject should be given to botanists? In case you undertake to revise the genus, I should be glad to procure all the material obtainable here for you.”5

Engelmann responded with a brief postcard: “Too early to work up Carya, but we must go on gathering material.”6 The epistolary trail with Engelmann ends there, although Sargent, writing two decades later, recalled that Letterman made substantial collections for Engelmann near Allenton and that those collections included “many notes on the Oaks and Hickories.”7

Entirely Overlooked

For his part, Sargent didn’t seem especially interested in the hickories during the census years, and he wouldn’t begin to wade into the subject until an 1889 Garden and Forest article, where he attempted to parse out whether the genus should be called Carya, Hicoria, or Hicorius, opting for the final option.8 An unattributed editorial ran after this nomenclatural treatment, celebrating the hickory as “purely an American tree,” given that none of the Asian species were known to Western botanists at the time. As the “conductor” for the magazine (essentially the publisher), Sargent must have conceded the general points, including, quite notably, an admission of taxonomic confusion. “More Americans know the Hickory-tree when they see it than any other of our trees,” the author wrote. “That is, they know generally, the Hickory, without distinguishing the different species, which is hardly surprising, since botanists themselves are often perplexed over questions concerning the proper limitations of these species.”9

Even so, when Sargent covered the genus in the seventh volume of Silva of North America, published in 1895, he sounded little taxonomic alarm, although he footnoted a new variety of pignut hickory (what he called Hicoria glabra var. villosa), based on a tree Letterman had documented in Allenton, and he offered passing descriptions of several unnamed hybrids. Yet, hickories weren’t alone in escaping Sargent’s taxonomic scrutiny; his research interests had just begun shifting from nomenclatural synthesis to novel taxonomy. Over the preceding years, Sargent had described as few as twenty-one new taxa for an assortment that included firs (Abies) and false box (Gyminda)—not counting nomenclatural transfers like Carya to Hicorius. In 1895, however, Sargent proposed another fourteen names—many of them oaks (Quercus)—suggesting he was becoming more confident of his own taxonomic eye. Those numbers continued to grow, and by 1907, he had added over three hundred names in Crataegus alone.

According to Sargent’s correspondence records (which become more consistent in the Arboretum archive in 1902 when he began saving carbon copies of his typewritten letters) his interest in hickories began gaining traction in 1908. That fall, around the time that hickory fruits would be ripening, he received a letter from a physician-turned-botanist named Robert T. Morris, who inquired about Carya buckleyi (now considered C. texana, the black hickory). Although the two men had corresponded about hickories the year before, Morris’s question about the black hickory seemed to awaken Sargent’s curiosity. “I confess that I, as well as all other botanists in recent years, have entirely overlooked this tree,” Sargent wrote back, referencing the taxon at large, rather than an individual plant. “The name does not appear in my Silva for some unaccountable reason as I was familiar with the paper [in the Proceedings of the Academy of Natural Sciences of Philadelphia] where it was first described … I shall be very glad of some of the nuts if you can spare them for me.”10

Morris had obtained a letter about the species from a grape breeder in northeastern Texas named Thomas Volney Munson. Sargent wrote to Munson immediately, even before responding to Morris, and offered to trade a selection of Chinese grape seedlings (grown from Ernest Henry Wilson collections) for fruit and herbarium specimens from the hickory.11 This exchange proved successful. Within three weeks, Munson had already shipped the specimens, along with a list of grape species he was interested in obtaining. Sargent, however, was rarely satiated, and he requested that Munson return to collect half-a-dozen specimens of branches with winter buds.12

The following March, Sargent rode the rails to Texas to see the inexplicable hickory himself. He also stopped in central Arkansas, where he botanized in the alluvial bottomlands near the town of Van Buren with the engineer of the municipal waterworks, George M. Brown, who was an avocational student of the flora. Munson and Brown were new collaborators for Sargent, and he took fondly to both. When he returned to Brookline, hickory propagules had already arrived from Brown. Sargent requested flowering specimens from both men—apparently his trip had missed the spring flush—and although he reminded them to gather fruiting specimens in the fall, Sargent ultimately returned to observe the plants himself. 13, 14 He visited both men in early October and also rendezvoused to talk about hickories with his longtime collector Benjamin Franklin Bush, who ran a general store near Kansas City, Missouri, and who had already proven himself a keen botanical observer for Sargent’s hawthorn research.

While he was travelling that fall, Sargent collected seed for at least nine Arboretum hickory accessions. Only one plant from this collecting trip is still growing at the Arboretum today, representing our oldest accession of the nutmeg hickory (Carya myristiciformis, accession 6048*C), a rare species, which Sargent collected in Arkansas. It is now an impressively straight-trunked specimen in the center of the hickory collection, growing not far from a smaller-statured black hickory (C. texana, accession 12892*C), sent from Brown in 1912, and a pignut hickory (C. glabra var. megacarpa, accession 18062*A), which Bush collected in southern Illinois that same year. Sargent’s enthusiasm was officially brimming.

Hickory Problems

If the unusual black hickory in Arkansas initially sparked Sargent’s concerted investigation of the genus, publication projects breathed oxygen onto the flame. While Sargent began working on his first edition of the Manual of the Trees of North America, distilling his work on the fourteen-volume Silva into one comprehensive guidebook (published in 1905), he began simultaneously proposing and describing new taxa in serialized publications titled Trees and Shrubs: Illustrations of New or Little Known Ligneous Plants. These were released incrementally, and his research on hickories would appear in the final installment, published in 1913. As the publication date approached, he began firing off letters to collectors, urging them for information about hickories. Many of the correspondents were recent hawthorn collaborators—tried and tested in their ability to field ceaseless requests—although Sargent even turned to his old census agents, perhaps because their trees were already growing in the Arboretum collection. “You used to be very keen about Hickories and I hope that you will have a relapse of the Hickory fever and make large collections again,” he wrote to Letterman in 1911, even though the two hadn’t corresponded significantly over the intervening years. “The genus has got to be reworked and I am getting together as much material as possible for this purpose that it may make a better showing in the new edition of my Manual than it does in the first edition.”15 He also wrote to Ridgway the same year, and Ridgway responded with characteristically meticulous and detailed handwritten notes, and professed enthusiasm for the project. “I have long been convinced that the genus is in sad need of overhauling,” he wrote, “and feel sure there are several more good species than are recognized in the books.”16

When Sargent ultimately published his treatment on the genus in 1913, he proposed seven new species or hybrids along with an additional thirteen varieties—marking his first published effort to disentangle and redefine taxonomic parameters within the hickories. (One of these hybrids, Carya × brownii, was based on an individual tree in the bottomlands of the Arkansas River, where it had puzzled Sargent and Brown back in 1909.) Yet this research on the hickories still proved unsatisfactory. Harbison—Sargent’s faithful southeastern collector—had made extensive collections of hickories the same fall the report was published. “I must say the more I see of them the more confused I become,” Sargent wrote about material Harbison had sent from Georgia and Alabama, typing his frustrated missive on New Year’s Eve. “It is evident, I think, that we cannot depend much on the fruit as I once supposed we could and that we must try for other characters, bark, habit, location, habitat, winter-buds, pubescence, etc. I do not suppose that there are a great many species but the trouble is to limit what there are. It seems to me that it will be impossible to properly know them without a great deal more field observation.”17

Notes like this became a recurring refrain over the next several years, as he repeatedly asked Harbison, Palmer, and others for additional information about specimens that had arrived. Sargent would ultimately publish his final taxonomic treatment of the genus in 1918, when it appeared in the Botanical Gazette. He proposed more than twenty additional taxa, many of them varieties and forms. By the number of proposed names, this placed hickories in the top three genera that Sargent had studied, behind only oaks and, of course, hawthorns.

Sepia photograph of man standing beside tree in winter
Sargent based his description of Carya × dunbarii on herbarium specimens from this tree, which John Dunbar had observed near Golah, New York. Richard Horsey, who worked with Dunbar at the Rochester Parks Department, photographed the tree and an unnamed man (could it be Dunbar himself?) in December 1918, shortly after publication of Sargent’s final report. Arnold Arboretum Archives

Sargent closed that final report by describing thirteen individual trees that had been observed by John Dunbar, the assistant superintendent of the Parks Department in Rochester, New York. Sargent provided precise notes about the color of the branches and the shape of the fruit. None of these thirteen plants resulted in accessions that are still growing in the Arboretum collection, although we still have eight plants (representing seven unique wild provenances) from Dunbar and his collaborator Bernard H. Slavin. Sargent praised the collectors and noted that no region had been more “carefully examined” for hickories than western New York. To Sargent, the discovery of confounding individuals there simply proved that other regions needed to be studied with the same rigor. If so, he suspected additional taxa would be discovered.

Nevertheless, hickories faded from Sargent’s correspondence, and he would never publish another taxonomic treatment of the genus. Whether this report absolved what Sargent described as the “hickory problem,” however, remains unclear. Several months before the report was published, he wrote a letter to Reginald Somers Cocks, a professor at Tulane University, who had been a frequent correspondent on the genus. “I have about finished up what I can do with Carya,” he wrote, “not a very satisfactory work.”18

More than American

Notably, during much of this period, hickories were one of the few tree genera that appeared unique to the eastern North American flora. In the unattributed Garden and Forest article from 1889, the author—again, presumably articulating ideas approved by Sargent—had described the wood and fruits in superlative terms. “As a nation we owe much to the Hickory tree, and we have good and just reason to be proud of it,” the author wrote, even suggesting that the lightweight yet durable carriages crafted from hickory had allowed equestrian breeders to develop the American trotting horse, “that race of horses which every American looks upon in his heart of hears with joy and admiration.”

Then, in 1915, Sargent received herbarium specimens of a Chinese hickory from the collector Frank Nicholas Meyer, who had first observed the fruits being sold at a market in Hangzhou, in eastern China. Sargent acknowledged receiving the specimens in a letter to Meyer the following January, and, of course, he requested more information about the size and abundance of the trees, not to mention photographs.19 Sargent’s intrigue about the discovery, however, is perhaps most evident in his account of the species in Plantae Wilsonianae. Sargent edited the three volumes, published between 1913 and 1917, yet of nearly eight hundred names pro – posed for new Chinese plant taxa (not counting nomenclatural transfers), most came from other Arboretum staff—prominently Alfred Rehder and Ernest Henry Wilson—as well as European colleagues like Camillo Schneider and Bernhard Koehne. Sargent authored only seven new names: six hawthorns and one hickory—what he called Carya cathayensis.

Trnk of shagbark hickory showing distinctive bark
Trunk of Chinese hickory

“Since the finding in China of a species of Liriodendron [tulip tree] and of Sassafras, previously believed to be monotypic genera of eastern North America, no addition to our knowledge of the distribution of the trees of the northern hemisphere is so important and interesting as Mr. Meyer’s discovery of a representative of the genus Carya in Asia,” Sargent declared in the publication, noting that progressively few genera appeared unique to eastern North America. “In China,” he continued, using a tone that could suggest a trace of disappointment, “there are many endemic trees.”20 Strangely, Sargent never acquired seed of this species from Meyer— perhaps suspecting they would be unable to grow at the Arboretum, given that it was discovered in the humid subtropics—and the only material ever collected (by Peter Del Tredici in 1989) never made it out of the greenhouse. It is currently on the list of desiderata for the Campaign for Living Collections.

Confidence in the Commonplace

Botanists would eventually begin consolidating many of the hickories Sargent had named. Because so many of the taxa were varieties, many of the names have been dropped in recognition of more morphologically diverse conceptions of each species. “Phenotypic variation from tree to tree is often considerable and difficult to quantify,” Donald Stone wrote in his treatment of the American species in the Flora of North America, published in 1997. “Most of this variation undoubtedly results from adaptation to local and regional conditions; hybridization has probably played a subtle role as well.”21 Stone included eleven species—down from the fifteen in Sargent’s final report—and referenced another seven species globally (most in eastern Asia, one in Mexico), although these numbers have fostered ongoing debate.22

In the spring of 1918, as Sargent was wrapping up work on his final hickory report, he wrote to Harbison, suggesting that certain hickory species had been neglected by botanists, given their general abundance and familiarity.23 It was this fundamental spirit that inspired what must be, even still, one of the most widespread and detailed morphological studies of the North American members of the genus—an impossible endeavor without the nuanced observations by Sargent’s cadre of mail correspondents. This collaborative effort also provided the centenarian core for the Arboretum’s robust collection of hickories, which was one of our first to be accredited by the American Public Gardens Association’s Plant Collections Network in 2002 (back when the network was known as the North American Plant Collections Consortium). Current field-collecting efforts continue to prioritize the genus, maintaining the intellectual passion of Sargent and his collaborators long ago: the confidence that even among the “plants which have been considered too common to collect,” something new can always be discovered.


1. Sargent, C.S. 1914. Sargent to T.G. Harbison, 2 March 1914 (volume 8, page 8). Charles Sprague Sargent (1841– 1927) papers, Arnold Arboretum Horticultural Library, Harvard University. (All Sargent correspondence below from the same archive, unless otherwise noted.)

2. Sargent to E.J. Palmer, January 19, 1915 (volume 8, page 308).

3. For the term “special agent” applied for collectors other than Sargent himself, see Sargent, C. S. 1902. Silva of North America, 13 (pp. 79–80.)

4. Ridgway, R. 1882. Notes on the native trees of the lower Wabash and White River valleys, in Illinois and Indiana. Proceedings of the United States National Museum, 82(1): 49–88.

5. Letterman. G.W. 1881. Letterman to G. Engelmann, April 12, 1881. Engelmann papers, Missouri Botanical Garden.

6. Engelmann, G. 1881. Engelmann to G.W. Letterman, April 14, 1881. Engelmann papers, Missouri Botanical Garden.

7. Sargent, C. S. 1902. Silva of North America, 13 (pp. 79–80). Boston and New York: Houghton Mifflin and Company.

8. Sargent, C.S. 1889. Notes upon some North American trees—XI. Garden and Forest, 2(83): 459–460.

9. Anon. 1889. The shell-bark hickory. Garden and Forest, 2(83): 460–461.

10. Sargent to R.T. Morris, October 21, 1908 (volume 6, page 161).

11. Sargent to T.V. Munson, October 19, 1908 (volume 6, page 160).

12. Sargent to T.V. Munson, November 7, 1908 (volume 6, page 190).

13. Sargent to G.M. Brown, March 31, 1909 ( volume 6, page 383).

14. Sargent to T.V. Munson, March 31, 1909 (volume 6, page 384).

15. Sargent to G.W. Letterman, June 7, 1911 (volume 7, page 122).

16. Ridgway to C.S. Sargent, August 6, 1912.

17. Sargent to T.G. Harbison, December 31, 1913 (volume 7, page 908).

18. Sargent to R. S. Cocks, June 19, 1918 (volume 9, page 296).

19. Sargent to F. N. Meyer, January 17, 1916 (volume 8, page 618).

20. Sargent, C. S. (Ed.). 1917. Plantae Wilsonianae, 3. Cambridge: The University Press

Citation: Damery, J. 2018. Hickory fever: Doing taxonomy by mail. Arnoldia, 76(1): 32–43.

21. Stone, D. E. 1997. Carya. Flora of North America North of Mexico, 3. New York and Oxford: Flora of North America Association.

22. Zhang, J.B., et al. 2013. Integrated fossil and molecular data reveal the biogeographic diversification of the eastern North American disjunct hickory genus. PLOS ONE, 8(7): 1–13.

23. Sargent to Harbison, June 19, 1918 (volume 9, page 294).

Jonathan Damery is Associate Editor of Arnoldia.