Osage Orange—God's Gift to the Prairie Farmer

"this curious fruit, which, when first discovered lying neglected beneath the tree, led the voyagers to fear and report it as a poison" wrote Thomas Nuttall (1842). Pete unseth photo.

In March of 1804, Meriwether Lewis, co-captain with William Clark of the Corps of Discovery, stopped at the home of trader Pierre Chouteau in St. Louis (Missouri Territory). The Chouteau brothers were supplying their expedition, which would depart in May, but this visit was for another matter. Lewis wanted to see Chouteau's garden.

President Thomas Jefferson had appointed Lewis expedition botanist. He was to study and record "the soil & face of the country, it's growth & vegetable productions, especially those not of the U.S. and the dates at which particular plants put forth or lose their flower, or leaf" (source). Given this assignment, there was good reason to visit Chouteau. The trader had lived in Louisiana Territory since birth, knew the Osage Indians well, and was familiar with their use of native plants, some of which he had planted in his garden.

Pierre Chouteau; Missouri Historical Society.

Lewis took cuttings from Chouteau's trees, and sent them to Jefferson, with a letter of explanation:

"I send you herewith inclosed, some slips of the Osages Plums, and Apples. I fear the season is too far advanced for their success. Had I earlyer learnt that these fruits were in the neighbourhood, they would have been forwarded at a more proper time ... I obtained the cuttings, now sent you, from the garden of Mr. Peter Choteau (1), who resided the greater portion of his time for many years with the Osage nation ..."

In his letter Lewis also explained the value of the Osage Apple (today's Osage Orange), presumably learned from Chouteau. "So much do the savages esteem the wood of this tree for the purpose of making their bows, that they travel many hundred miles in quest of it." Decades later, the tree would be highly esteemed by farmers as well—on the great sea of grass to the west.

In 1810 or thereabouts, another botanist visited Pierre Chouteau's garden. Thomas Nuttall, recently arrived from England, took a particular interest in the Osage Apple, which had not yet been introduced to science. He published the new species in 1818, naming it Maclura aurantiaca to honor his friend, geologist William Maclure; aurantiaca means orange, referring to the color of the wood. In 1906, this was replaced with the currently accepted name, Maclura pomifera (2).

"The wood is very heavy and of a Saffron yellow ..." wrote Nuttall (1818). Fernando Lopez Anido photo.

Nuttall's description was incomplete. For one thing, he hadn't seen any male flowers (Maclura flowers are unisexual; trees have either male or female flowers). This did not keep him from publishing, for the female flowers, and especially the fruit, are what make the species so distinctive.

Nuttall noted that Maclura's female flowers are arranged in dense globose clusters. Though tiny, each one has a style nearly an inch long. At maturity the 1-seeded fruits of the many flowers in a cluster coalesce into a "compound berry" (now known as a multiple fruit) containing "pulp nearly as succulent as that of an orange, sweetish and perhaps agreeable when fully ripe" (Nuttall also lacked information concerning edibility).

Maclura's female inflorescence of numerous tiny flowers, each with a long narrow style. H. Zell photo.

The Osage Orange is a multiple fruit (Nuttall's compound berry). H. Zell photo.

Multiple seedlings from a multiple fruit. Cbarlow photo.

Thirty years later, Nuttall, by then an acknowledged expert on the North American flora, was engaged in a monumental project—three supplemental volumes to François-André Michaux's North American Sylva (forest trees). Among the added species was Osage Orange. It appeared in the first volume, with a lengthy description and two beautiful plates.

Osage Orange, also called Bois d'Arc meaning Bow Wood (3): branch of a male plant on right, note the stout thorns; female flowers with long styles lower left; source.

Osage Orange; cross-section showing flowers united to form a multiple fruit; source.

Nuttall now had better information about edibility: "The fruit, when ripe, is succulent, has a sweetish but insipid taste, and is somewhat acrid. As far as we know, it is not eaten by any animal" (4). Also of interest (and timely) was an item in his description of the wood: "Another important use of the Maclura ... is that of forming live fences or hedges, for which purpose it is well adapted, as it bears cutting, grows close, and is very thorny."

OSAGE ORANGE—Can any one tell us more of this tree? We are desirous of having our columns made the vehicle for communicating information of any material that may be made valuable for hedging. This tree ... seems well adapted for that purpose; and if any has been used in Missouri or elsewhere, it would be a great favor to have an account of it furnished us. The Prairie Farmer, Vol. 1 No. 1, January 1, 1841.

While Nuttall was finishing his first volume, John A. Wright, a real estate speculator in the muddy young town of Chicago, was pursuing his dream. He wanted to help farmers who were struggling on the great sea of grass stretching a thousand miles to the west—"an open plain, so barren of timber, so huge of expanse as to bewilder, often frighten, them." The accumulated wisdom of settlers in wooded country to the east was of little use. Instead of clearing trees, prairie farmers toiled to break thick tough sod. And in the absence of trees, wood had to be imported at great expense (Lewis 1941).

No trees? Use sod! Soddy (sod house) in 1901; photographer unknown.

The need for helpful information was dire. Toward this end, Wright drummed up financial support for a non-partisan apolitical newspaper specifically for farmers. Though he had never farmed himself, he agreed to be the editor. On January 1, 1841, the first issue of The Union Agriculturalist and Western Prairie Farmer (soon shortened to The Prairie Farmer) was published (5).

On the front page, Wright appealed to readers for help:

TO THE PRACTICAL FARMER—Upon you we must rely for the matter that is to make this paper interesting and valuable. ... What we wish is this—as soon as any one obtains any valuable agricultural information, a recipe, a plan, or any other matter that would be adapted to our paper, that he would sit down immediately and communicate it. In this manner communications will be more to the point than if writers delay till they can collect several facts. ... if as soon as a farmer obtains one fact, he sends it, it will be what we want—"short and sweet."

Wright was well aware that some, perhaps many, would hesitate to contribute:

Many farmers may perhaps decline communicating their knowledge, because they may feel themselves incompetent to write for publication. To such we would say, that we most earnestly request you to send us articles, and should there be a word mis-spelt, or a sentence that might be improved by a little alteration, we will use our endeavors to make it right. What we want are facts—and perhaps a fact a farmer might possess, and which he declines sending, because he may perhaps not have enjoyed advantages of education in early life, might be of more service to the West, than all the matter we might publish in several numbers [issues].

Among Wright's passions was fencing, understandably. One of the biggest problems farmers faced was marauding wildlife and livestock. The cost of imported wooden fence was prohibitive and wire fences of the day—horizontal unarmed strands—were ineffective. So farmers tried hedges, also called living fences. Wright had read in the Hartford Silk Culturalist that Osage Orange trees made excellent hedges, and included that article in his paper. The final sentence was especially persuasive:

On the best authority, I am assured that the trees of the Osage Orange, when set at the distance of fifteen inches asunder, make the most beautiful as well as the strongest hedge fence in the world through which, neither men nor animals can pass.

Osage Orange—gift from God? JM DiTomaso photo (CC 3.0)

Osage Orange was soon a hot topic, with readers begging for information on where to buy viable seed and young plants. Fortunately Professor JB Turner of Illinois College had taken an interest. In the 1830s he had crossed "these beautiful prairies for some thousands of miles on horseback" concluding that whoever produced cheap effective fencing would go down in western history as the "greatest moral, intellectual, social and pecuniary benefactor." Perhaps in hopes of being that benefactor, Turner began a study of Osage Orange, periodically reporting his progress in The Prairie Farmer.

By 1848, Turner was convinced that "the Osage Orange is the shrub that God designed especially for the purpose of fencing the prairies." That November he announced he had plants for sale. He didn't know the exact price, but estimated a hedge 80 rods long (c. 1300 ft) would cost less than $15. By 1853 the price had dropped to $25 per mile, while a wooden fence "would cost $300 a mile and would be gone in 12 years" [due to prairie fires].

But in spite of its many advantages and perhaps divine origin, the Osage Orange hedge fell out of favor after just thirty years, a victim of innovation. JF Glidden of DeKalb, Illinois, had come up with a clever solution for wire fencing—barbs. Business took off immediately. The year after it started as a one-man operation, 70 men were producing three tons of fencing per day! (PF May 1875).

Both cheap effective wire fences and Osage Orange seeds were available in February 1875.

Note the clever design—"two No. 12 wires on one of which are wound the barbs ... they are then twisted holding the barbs immovable in their places" (May 1875).

Many hedges were removed and replaced with barbed wire. Others were simply abandoned. But Osage Orange trees did not disappear. Some were scavenged for fenceposts ...

Maclura posts are dense, strong, and resistant to rot and insects. Original source unknown.

... and Osage Orange hedges are still planted ...

Maclura hedge in Primorsko, Bulgaria; photo by Katya.

... and the legacy of the prairie farmers' blessing is still with us.

Thanks to prairie farmers, Maclura pomifera (dark green) occurs far beyond its original range (light green); from USDA, and Nelson et al. 2014 (6).

Notes

(1) Chouteau signed his letters apropos the recipient—Pierre Chouteau, Pedro Chouteau, and Peter Chouteau for French, Spanish, and English speakers.

(2) Osage Orange has a complicated nomenclatural history. It was first published in 1817 as Ioxylon pomifera by French naturalist Constantine Samuel Rafinesque, who then made a series of name changes: Toxylon pomiferum in 1818, Joxylon pomiferum in 1819. In the meantime Thomas Nuttall named it Maclura aurantica (1818). This became the accepted name perhaps because of Nuttall's greater botanical stature. In 1906 it was renamed M. pomifera, perhaps related to Rafinesque's first-published name. See Smith 1981. Further complications can be found in Reveal & Musselman.

(3) Maclura pomifera has many common names, including Osage Orange, Hedge Apple, Yellow Wood, Monkey Brains, Bow Wood, Bois d'Arc, Bodark and more.

(4) While Osage Orange pulp isn't edible, the seeds are. From Mike on Flickr: Osage orange trees are a magnet for squirrels. They typically sit on the ground at the base of the tree, or on a wide branch up in the tree to disassemble their prize, getting at the seeds. Piles of shredded hedge apples are a sure sign of squirrels in the area. The seeds are edible by people, but one must do like the squirrels, and remove the slimy husk to pick them out of the pulpy fruit.

(5) The Prairie Farmer is still being published, including a digital edition.

(6) The native range of Maclura pomifera is debated and probably irresolvable (Smith 1981).

Sources in addition to links in post

Earle, AS, and Reveal, JL. 2003. Lewis and Clark's Green World; the expedition and its plants. Farcountry Press.

Foley, WE. 1983. The Lewis and Clark Expedition's silent partners: the Chouteau Brothers of St. Louis. Missouri Historical Review 77:131–146. SHSMO

Lewis, L. 1941. Prairie Farmer, its beginnings. Prairie Farmer 11:5–17 (centennial edition). Illinois Digital Newspaper Collections.

Michaux, F-A, Nuttall, T, Hillhouse, AL, and Redouté, PJ. 1842. The North American Sylva; or, A Description of the Forest Trees of the United States, Canada, and Nova Scotia ... Vol. 1. BHL

Nelson, G, et al. 2014. Trees of Eastern North America. Princeton University Press.

Nuttall, T. 1818. The genera of North American plants and a catalogue of the species, to the year 1817 [Maclura 2:233]. BHL

Rafinesque, CS. 1817. Description of the Ioxylon pomiferum, a new genus of North American tree. American Monthly Magazine and Critical Review 2:118–119. Google Books

Reveal, JL, and Mussulman, JA. The Osage Orange; Maclura pomifera, in Discover Lewis & Clark (Lewis & Clark Trail Alliance). Accessed December 2024.

Tree Following: Killer Cottonwood in Utah

On a hot afternoon several weeks ago, I pulled into Hittle Bottom Campground on the Colorado River in southern Utah. After parking in the only site with shade, I opened the windows, put screens in place, inserted $10 in the payment envelope, and started for the pay station. But I was stopped in my tracks by a Killer Tree, right next to our campsite!

The area around it had been cordoned off with orange caution tape, but I checked carefully to make sure we were safe. Indeed everything was fine. We were out of range of falling limbs.

Click on image to view caution tape, marked by arrows.

The big cottonwoods that grow along lowland rivers in North America—Populus deltoides and P. fremontii —are infamous for dropping large dead branches. As the Colorado AAA has observed:

No one writes poems about “under the spreading cottonwood tree” because it can actually be dangerous to sit under a cottonwood in high winds due to breaking branches.

The technical term for this is "dieback".

Some cities (Denver for example) ban these cottonwoods in part because of dieback. They grow fast (to six feet per year!) and are relatively short-lived, so falling limbs will be a problem. And they grow roots toward and into reliable water sources such as city water and sewer lines! This is an impressive adaptation for the trees but a problem for us (source).

The Hittle Bottom Campground has no water aside from the river, so managers don't worry about cottonwood roots invading plumbing. But dieback is a problem, hence the caution tape. Of course I wanted photos, so I risked my life so in the absence of imminent danger (the day was calm) I stepped over the tape to commune with the Killer Tree.

Zig-zag form due to lost branches.

The bark was especially photogenic, even with tape.

This is Fremont's Cottonwood, named to honor the famous explorer and surveyor John Charles Fremont. However the honor probably celebrates another of his achievements, one less widely known—botanical discovery! Fremont was not a taxonomic expert but he knew how to collect plants. And collect he did—on the order of two thousand specimens. Among these were at least 165 species new to science, some 40 of which were named in his honor. For more about Fremont's botanizing, see JC Fremont was here.

On the afternoon of March 30, 1846, Fremont and his party "encamped on Deer Creek, another of these beautiful tributaries to the Sacramento [River, in California]. Mr. Lassen, a native of Germany, has established a rancho here ...". They stayed for five days, during which time Fremont collected plants, including a cottonwood. He suspected it might be a new species, as he had noted the previous year when he was in southern Utah (no collection was made or survived).

Fremont's 1846 specimen from "Deer Creek at Lassens" (Gray Herbarium). He collected both male (above) and female (below) flowers, demonstrating knowledge and care in collecting plants.

Typical of field botanists at that time, Fremont relied on experts for identification. He sent many of his collections to the leading American plant taxonomist—Asa Gray at Harvard. Gray often passed along western specimens to his colleague, Sereno Watson, who was more familiar with that flora. It was Watson who named and described Populus fremontii.

Sereno Watson (Wikimedia). A colleague described him as "tall, very erect, [with] good features, a high-bridged nose, and a carefully tended beard of great length and whiteness. Almost to the end of his life he walked with a brisk elastic step suggesting physical energy remarkable for a man of his years."

In his 1875 paper, Watson distinguished P. fremontii from its close relatives "especially by the remarkably developed torus" (now called floral disc). He also noted that young growth tended to be somewhat hairy. In contrast, the similar P. deltoides has smaller floral discs and young growth is not hairy.

A century later, James Eckenwalder, expert on the genus Populus, reached the same conclusions, recognizing the larger floral disc and often hairy young growth as distinguishing features for Fremont's Cottonwood (see also his treatment in Flora of North America).

Populus fremontii from Sargent's 1896 Silva of North America; added enlargement shows female flower with floral disc—thought to have evolved from petals and sepals.

Fremont's Cottonwood with capsules and young leaves (TreeLib, J Morefield photo).

Mature leaves and bark, Fremont's Cottonwood (TreeLib).

These last photos are included in part to thank Blake and Nathan Willson for their wonderful Tree Library website—"a digital platform for teaching and studying trees with a focus on promoting awareness and understanding of trees and their global importance to the environment."

Fremont's Cottonwood, Rio Grande, New Mexico. "Trees are our silent partners, sensing us as we move about, providing shelter, offering us beauty, and nurturing and protecting the earth." (TreeLib)

Addendum, 23 Oct 2024. Posch, BC, et al. (2024) found Populus fremontii to be super efficient at leaf cooling (via transpiration) even when temperatures exceed 48 °C (118º F)! But water must be available. Even a minor disruption in availability will shut down cooling, causing leaves to overheat. See Intensive leaf cooling promotes tree survival during a record heatwave. 

https://doi.org/10.1073/pnas.2408583121

Sources, in addition to links in post

Eckenwalder, JE. 1977. North American cottonwoods (Populus, Salicaceae) of sections Abaso and Aigeiros. J. Arnold Arboretum 58:193–208 [P. fremontii p. 198-200] BHL.

Fremont, JC. 1887. Memoirs of my life: including in the narrative five journeys of western exploration during the years 1842, 1843-4, 1845-6-7, 1848-9, 1853-4 Internet Archive.

Sargent, CS. 1896. The silva of North America: a description of the trees which grow naturally in North America exclusive of Mexico. Vol. 9 (P. fremontii p.183 ...) BHL.

Watson, S. 1875. Revision of the genus Ceanothus, and descriptions of new plants ... Proceedings American Academy of Arts & Sciences. Vol. 10 (P. fremontii p. 350) BHL.

This is my October contribution to the monthly gathering of Tree Followers, kindly hosted by The Squirrelbasket.

South Dakota Trees: Black Walnut

Black Walnut with spring leaves—its "yearly trick of looking new" (Philip Larkin, The Trees). Union Grove State Park, South Dakota.

Walnuts from a previous year, still unopened. Is extreme toughness adaptive?

Continuing my quest to get to know South Dakota's trees, I chose Black Walnut (Juglans nigra) for this month's tree-following. It's native to the state but barely, probably just in the far east. This is another deciduous hardwood that's common in the midwestern and eastern USA, but rare in South Dakota. Humans have long contributed to the spread of these species, so it can be difficult to pin down their "native" range.

Black Walnut trees can reach 150 ft in height. On open sites the crown is large and rounded. In forested habitat it's smaller, atop a tall mostly unbranched trunk. 

Black Walnut is popular in landscaping; Victoria, British Columbia (TreeLib).

Juglans nigra was once "a dominant and majestic canopy species of primeval midwestern and southeastern forests." But with clearing for agriculture, and harvest for railroad ties, gunstocks, log cabins, furniture, ship-building and more, it became much less common (GoBotany). The venerable giants—to 6 or 7 ft in diameter—are gone. Even so, Black Walnut wood is widely available and quite popular—prized for its dark grain (more information at The Wood Database).

Black Walnut in cross section; photo by Roger Culos.

Black Walnut bowl and photo by Joe Nestlerode.

Juglans nigra leaves are alternate, but often cluster at branch tips and appear whorled (MWI).

Black Walnut usually can be recognized by its leaves, which are long (to 6 dm) and pinnately compound with 8–23 leaflets (terminal one often reduced or lacking). Leaflets are lanceolate, to 15 cm in length, and have serrate margins.

Carl Linnaeus, who named and described the species in 1753, included leaf features in the polynomial name: Juglans foliolis lanceolatis argute serratis—a Juglans with lanceolate leaves with serrate margins. Did Linnaeus mistake leaflets for leaves? Perhaps there was no such distinction in his day.

Black Walnut in Linnaeus's Species Plantarum (1753). Note "nigra" in fine print on right.

In the image above, "nigra", "alba" and "regia" on the page margin hint at a revolution underway. The long descriptive polynomial names were being replaced with binomials (still in use). Species Plantarum is considered the first major botanical work to use binomials consistently. This is where Juglans foliolis lanceolatis argute serratis; exterioribus minoribus became Juglans nigra L. (L. refers to Linnaeus, the authority).

Juglans nigra L. from The Linnaean Herbarium, with permission. Linnaeus did not cite a type specimen in his description, so this one was selected as the lectotype (Reveal et al. 1987).

Like all walnut species, Juglans nigra has unisexual flowers and trees bear flowers of both sexes (i.e., are monoecious). Flowers are inconspicuous—small, yellowish to greenish, with no petals and only tiny sepals. Males form catkins (elongate pendulous clusters) to 10 cm long, with numerous flowers. Female flowers occur in little clusters of 1–4 in leaf axils (where the leaf stem attaches to the branch).

Catkins of male flowers, each with numerous stamens (MWI).

Three female flowers in a leaf axil, each with 2 feathery stigmas (TreeLib).

A female flower has a single pistil. With fertilization, it matures to become ... well ... that depends on whom you ask.

 Juglans nigra fruit, fibrous covering partly removed. Is this a nut? drupe? pseudodrupe? (Plant Image Library)

In their treatments of the Black Walnut, early botanists just described the fruit. The first to do so may have been Mark Catesby, an English naturalist who studied the flora and fauna of the American colonies. In his Natural History of Carolina, Florida and the Bahama Islands (1731) he wrote:

"The thickness of the inner shell requires a hammer to break it. The outer shell is very thick and rough on the outside. The kernels are very oily and rank tasted; yet, when laid by some months are eat by Indians, squirrels, etc." [Kernels are seeds, also called nutmeats.]

Illustrations in Catesby's book "were etched by the author"; plants and animals often were paired, e.g., Black Walnut and American Redstart (relative sizes of fruits and bird are correct) (BHL).

In his 1819 American Sylva, François-André Michaux (featured in this post) provided a bit more detail:

"The husk is thick, and ... when ripe it softens and gradually decays. The nut is hard, somewhat compressed at the sides, and sulcated [with narrow grooves]. The kernel, which is divided by firm ligneous partitions, is of a sweet and agreeable taste, though inferior to that of the European Walnut." 

Black Walnut, by the great botanical illustrator Pierre-Joseph Redouté, in Michaux 1819 (BHL). Male flowers upper left; fruit with green husk lower right next to brown nut.

However it wasn't long before botanists were attempting to assign fruits to defined types. Asa Gray, the eminent Harvard professor of botany, included a system of fruit types in his 1868 Lessons in Botany and Vegetable Physiology. Now 156 years later, it's still in use because botanists haven't come up with anything better. This is not for lack of trying (see Judd et al. 2002, for example).

So what did Professor Gray call the walnut? Well, actually ... he hedged!! In his New Manual of Botany. A handbook of the flowering plants (1908) he called it a "a kind of dry drupe". Dry drupe? But Professor, you defined a drupe as having a fleshy outer part and hard inner part, both derived from the pistil. You provided the cherry, plum, and peach as familiar examples.

As Professor Gray demonstrated, the walnut is not easily categorized. And it's not alone—more than a few fruits confound us in this way.

Parts of a walnut: husk, shell (nut), nutmeat (seed). Wild Harvests.

Some botanists take a strict approach: a fruit must develop from a pistil. This is where the fruit of the walnut—specifically the husk—causes problems. "[It] superficially resembles a drupe, with a hard 'stone' surrounded by a soft, often fleshy husk. The husk, however, is not part of the fruit wall (it develops from the involucre and calyx), and the fruit is actually a nut." (Juglandaceae in Flora of North America).

The Wikipedia Walnuts article mostly agrees, but calls them "accessory fruit because the outer covering [husk] of the fruit is technically an involucre and thus not morphologically part of the carpel [pistil]; this means it cannot be a drupe but is instead a drupe-like nut."

Other botanists are more broad-minded. A fruit with a (relatively) soft outer part and hard inner part can be a drupe, no matter the origins of the parts. Some avoid the controversy altogether by calling the walnut fruit a "drupe or nut" or explaining that it's a nut "but some experts call it a drupe."

That's more than enough discussion of disputed terminology. Let's turn now to something for which there is widespread and probably unanimous agreement. The Black Walnut is a tough nut to crack, in fact one of the toughest!

Cracking a Black Walnut Appalachian style (Blind Pig & the Acorn).

Black Walnut nutmeats are available commercially thanks to "high-tech" processing (video here). But there are alternatives. For those who aspire to collect, clean and crack Black Walnuts themselves, a wealth of helpful information is available online. The most common approach is a hammer, as Mark Catesby recommended nearly three centuries ago. Iowa State University Extension and Outreach explains:

"The hammer method involves placing the nut, pointed end up, on a hard surface and striking the point with the hammer until it weakens and splits into sections along its axis ... shattering of the kernels is often a problem. Shattering can be reduced by soaking the nuts in water for 1 or 2 hours before cracking. The soaking process allows the kernels to absorb enough moisture to become somewhat flexible, resulting in larger kernel pieces."

"Once split, use a pick or plier to remove the kernels inside." (ISU Extension & Outreach)

And for those of us with less patience, John Sankey includes a variety of tools on his Black Walnut Crackers webpage, with tips on use.

The Duke Black Walnut Nutcracker is highly-recommended ($78 on Amazon).

Sources, in addition to links in post

Catesby, M. 1731. Natural history of Carolina, Florida and the Bahama Islands. Volume 1 (Black Walnut p 67). "The illustrations were etched by the author from his own drawings and hand colored under his direction." Catesby also paid for printing. BHL

Gray, A. 1868. Gray's lessons in botany and vegetable physiology. NY: Ivison, Blakeman, Taylor & Co. (BHL).

Gray, A. Circa 1908. Gray's new manual of botany. A handbook of the flowering plants and ferns of the central and northeastern United States and adjacent Canada. NY: American Book Co. BHL

Judd, WS, et al. 2002. Plant Systematics, 2nd ed. Sinauer Associates, Inc.

Linnaeus, Carl. 1753. Species Plantarum 2, p. 997. BHL.

Michaux, F-A. 1819. The North American sylva, or A description of the forest trees of the United States, Canada and Nova Scotia. BHL

Nelson, G, et al. 2014. Trees of eastern North America. Princeton University Press.

Reveal, JL, et al. 1987. On the identities of Maryland plants mentioned in the first two editions of Linnaeus' Species plantarum. Huntia 7:209–246. PDF

South Dakota Tree-Following: le Chêne à gros acorn

"An Oak, whose leaves are as large, and which bears such large fruits, is well suited to attract the attention of lovers of foreign cultures, and to find a place in the parks and gardens of a large extent." FA Michaux, 1810 (translated from French). TreeLib photo.

In 1785, 15-year-old François-André Michaux traveled to America with his father, André Michaux, Royal Botanist to Louis XVI. They had been provided a commission and instructions to collect unusual plants and useful trees. The latter were especially valuable, as European countries were running out of wood. Like fossil fuels today, wood was critical for transport (e.g., large armadas of wooden ships!) and in manufacturing (charcoal for iron smelters, glassworks, and more).

Michaux the younger returned to France in 1790, as did his father six years later. Together they went to work on what would become the great Histoire des Arbres Forestiers de l’Amerique Septentrionale. It was published in 1810 in French by François-André alone, as his father had died in 1802 (subsequent references to "Michaux" in this post are to the younger). It would be published in English as The North American Sylva (1).

Quercus macrocarpa, Over Cup White Oak (today's Bur Oak). Michaux 1810; BHL.

Among their discoveries was an oak with exceptionally large acorns, the basis for the species name given by Michaux—macrocarpa. The common name at that time, Over Cup White Oak, refers to the sizable cup that sometimes nearly covers the nut. Unfortunately the wood was "inferior in quality to that of true white oak" (2).

Quercus macrocarpa is one of nearly 100 oak species in North America north of Mexico (3). While it's easy to recognize a tree as an oak (with leaves), trying to distinguish among oak species can be very frustrating. Many oaks hybridize, acorns often are lacking or immature, and the tiny flowers are similar among species and not useful in identification. Botanists generally rely on leaves and twigs. But leaves are variable, even on a single tree, so one must collect a representative selection of mature sun leaves (not shade) for identification. Twigs with mature buds can be helpful (FNA).

Male catkins (flower clusters) of Bur Oak, tiny male flowers in insert. Oak flowers are unisexual, and trees are monoecious (with flowers of both sexes). MWI photo.

In South Dakota however, we have it easy. Bur Oak is the only oak species native to the state. This lack of diversity is disappointing but it does make life simpler. And we will take a close look at our oak anyway. Nothing wrong with enjoying a tree.

Michaux considered the Bur Oak "a very beautiful tree ... its foliage appeared to me to be very thick and quite dark green. Its leaves, larger than those of other species which grow in the United States, often are 40 centimeters in length, and 20 centimeters at their widest part. They are crenellated at their summit ... and cut very deeply in their lower two thirds."

A classic Bur Oak leaf: crenulate at the tip, deeply lobed below, fiddle-shaped overall.

Gazing up through Bur Oak canopies is a lovely way to spend an afternoon.

All oaks have clusters of terminal and lateral buds at the tips of twigs, which helps in recognizing leafless oaks in winter. Older twigs of Bur Oak often have corky ridges.

Terminal and lateral buds clustered at tip of a Bur Oak twig. MWI photo.

Corky ridge on an older Bur Oak twig. Nature Manitoba.

An acorn is by definition the fruit of an oak; illustration from Cronodon. 

The fruit of the Bur Oak is, of course, an acorn—a nut in a cup. Those of the Bur Oak are usually distinctive: "The acorns, oval in shape, are also [like the leaves] larger than those of all other species of Oak trees found in North America ... These acorns are contained, up to two thirds of their length, in a thick, unequal cup, and whose edges are lined with loose and flexible filaments" (Michaux 1810).

The overlapping scales of the cup of the Bur Oak are bumpy (tuberculate). Those near the rim have elongate tips, which make the cup look fringed—the basis for another common name, Mossy-cup Oak. But the fringe may be absent, as Michaux noted. "Sometimes, however, when these Oaks are found in the middle of dense forests, or the summers are not very hot, these filaments [elongate tips] do not appear, so that the edge of the cup is completely plain, and appears as if folded internally."

Sometimes the cup nearly encloses the nut. Bur Oak acorns in Missouri. Grey Wanderer photo.

When I arrived at Newton Hills State Park in far eastern South Dakota last month, I secured a site in a small area for tent campers in an oak opening (Bur Oaks prefer open habitat). Having forgotten my trip to eastern Nebraska long ago, I was surprised by the stature of the Bur Oaks. Being a westerner, it's not what I'm used to.

Canopies composed of beautifully sinuous branches.

Another campground, more oaks.

Everything about them was photogenic, including the bark.

Quercus macrocarpa; from USGS digitized "Atlas of United States Trees" by Elbert L. Little, Jr. Source. This is a 1971 map; Bur Oak is now known to grow farther west in northeast Wyoming. 

Bur Oak has a large range, from New England through the Midwest and south nearly to the coast in Texas. Its western limit is near the Hundredth Meridian as far north as Nebraska. But it grows farther west and north in the Dakotas, Wyoming, Montana and Manitoba. In fact it's the most northerly of our native oaks, being the most cold tolerant (Nelson et al 2014). Less hospitable habitat may be reflected in stature (4). These are the Bur Oaks I know—scrappy little trees or even shrubs.

Bur Oaks in front of Ponderosa Pines, northeast Wyoming. Matt Lavin photo.

Western Bur Oak acorns are smaller than those of eastern trees; note thumb for scale. Matt Lavin photo.

Notes

(1) The American Sylva has a complicated history, with at least a dozen known editions in multiple printings and formats (Constantino 2018). Most recently (2017), the New York Botanic Garden published 277 color plates from the Sylva in The Trees of North America: Michaux and Redouté’s American Masterpiece.

(2) Not everyone agrees with Michaux. According to the Flora of North America, "Wood of Q. macrocarpa is similar to that of Q. alba [White Oak] and produces one of the best and most durable oak lumbers."

(3) North American oaks are divided into three sections: white, red, and golden. Bur Oak belongs to the white oaks, characterized by leaves with no bristles on the tips or lobes, acorns produced every year (if conditions allow), and acorn cups with tuberculate (bumpy) scales (Nelson et al. 2014).

(4) Smaller Bur Oaks in the west and northwest are sometimes recognized as Quercus macrocarpa var. depressa (see Tropicos for the name's origins). In a study of Q. macrocarpa in the Black Hills and parts of New Mexico, Maze (1968) saw evidence of past hybridization with the more southern Q. gambelii; ongoing hybridization is unlikely because today's species are not sympatric. Maze recognized hybrids based on leaf and cup morphology, not tree stature. However one hybrid was described as being shrubby. In Flora of North America, the smaller form is considered an endpoint in clinal (continuous) variation from east to west, but more study may support recognition of var. depressa.

Sources (in addition to links in post)

Costantino, Grace. 2018. Exploring the First American Silva. Biodiversity Heritage Library Blog.

Maze, J. 1968. Past hybridization between Quercus macrocarpa and Q. gambelii. Brittonia 20:321–323.

Michaux, François-André. 1810. Histoire des arbres forestiers de l'Amérique septentrionale. Paris, L. Haussmann. (Quercus macrocarpa p 34–35 and Plate 3). BHL

Nelson, G, et al. 2014. Trees of eastern North America. Princeton U Press.

This is my June contribution to the monthly gathering of tree followers kindly hosted by The Squirrelbasket. More news here.