English oak acornAcorns of the willow oak inSouth Carolina (from small to large, counterclockwise from center):Q. phellos (willow oak),Q. falcata (southern red oak; top right),Q. alba (white oak), andQ. coccinea (scarlet oak). Scale bar at upper right is 1 cm.Diagram of the anatomy of an acorn: A.)Cupule B.)Pericarp (fruit wall) C.) Seed coat (testa) D.)Cotyledons (2) E.)Plumule F.)Radicle G.) Remains ofstyle. Together D., E., and F. make up the embryo.
Theacorn is thenut of theoaks and their close relatives (generaQuercus,Notholithocarpus andLithocarpus, in the familyFagaceae). It usually contains aseedling surrounded by twocotyledons (seedling leaves), enclosed in a toughshell known as the pericarp, and borne in a cup-shapedcupule.[1][2] Acorns are 1–6 cm (1⁄2–2+1⁄2 in) long and0.8–4 cm (3⁄8–1+5⁄8 in) on the fat side. Acorns take between 5 and 24 months (depending on the species) to mature; see thelist ofQuercus species for details of oak classification, in which acornmorphology andphenology are important factors.
The wordacorn (earlierakerne, andacharn) is related to theGothic nameakran, which had the sense of "fruit of the unenclosed land".[3] The word was applied to the most important forest produce, that of the oak.Chaucer spoke of "achornes of okes" in the 14th century. By degrees, popularetymology connected the word both with "corn" and "oak-horn", and the spelling changed accordingly.[4] The current spelling (emergedc. 15th–16th century) derives from association withac (Old English: "oak") +corn.[5]
Ponies eating acorns. Acorns can cause painful death inequines, especially if eaten in excess.Sprouting acorn ofQuercus robur
Acorns play an important role inforest ecology when oaks are plentiful or dominant in the landscape.[6] The volume of the acorn crop may vary widely, creating great abundance or great stress on the many animals dependent on acorns and the predators of those animals.[7] Acorns, along with other nuts, are termedmast.
Wildlife that consume acorns as an important part of their diets include birds, such asjays,pigeons, someducks, and several species ofwoodpeckers. Smallmammals that feed on acorns includemice,squirrels and several otherrodents. One beetle species,Thorectes lusitanicus, also feeds on acorns.[8] Acorns have a large influence on smallrodents in theirhabitats, as large acorn yields help rodent populations to grow.[9]
Large mammals such as pigs, bears, anddeer also consume large amounts of acorns; they may constitute up to 25% of the diet of deer in the autumn.[10] In Spain, Portugal and theNew Forest region of southern England, pigs are still turned loose indehesas (large oakgroves) in the autumn, to fill and fatten themselves on acorns. Heavy consumption of acorns can, on the other hand, be toxic to other animals that cannot detoxify theirtannins, such as horses and cattle,[11][12] especially if eaten in excess.[13][14][15]
Thelarvae of somemoths andweevils also live in young acorns, consuming the kernels as they develop.[16]
Acorns are attractive to animals because they are large and thus efficiently consumed or cached. Acorns are also rich in nutrients. Percentages vary from species to species, but all acorns contain large amounts ofprotein,carbohydrates andfats, as well as the mineralscalcium,phosphorus andpotassium, and thevitaminniacin. Totalfood energy in an acorn also varies by species, but all compare well with other wild foods and with other nuts.[17]
Acorns also contain bittertannins, the amount varying with the species. Since tannins, which are plantpolyphenols, interfere with an animal's ability tometabolize protein, creatures must adapt in different ways to use the nutritional value acorns contain. Animals may preferentially select acorns that contain fewer tannins. When the tannins are metabolized in cattle, the tannic acid produced can causeulceration andkidney failure.[12]
Animals thatcache acorns, such as jays and squirrels, may wait to consume some of these acorns until sufficient groundwater haspercolated through them toleach out the tannins. Other animals buffer their acorn diet with other foods. Many insects, birds, and mammals metabolize tannins with fewer ill effects than do humans.
Species of acorn that contain large amounts of tannins are very bitter,astringent, and potentially irritating if eaten raw. This is particularly true of the acorns of Americanred oaks andEnglish oaks. The acorns ofwhite oaks, being much lower in tannins, are nutty in flavor; this characteristic is enhanced if the acorns are given a light roast before grinding.
Tannins can be removed by soaking chopped acorns in several changes of water, until the water no longer turns brown. Cold water leaching can take several days, but three to four changes of boiling water can leach the tannins in under an hour.[18] Hot water leaching (boiling) cooks the starch of the acorn, which would otherwise act like gluten in flour, helping it bind to itself. For this reason, if the acorns will be used to make flour, then cold water leaching is preferred.[19]
Being rich in fat, acorn flour can spoil ormolder easily and must be carefully stored. Acorns are also sometimes prepared as a massage oil.
Acorns of the white oak group,Leucobalanus, typically start rooting as soon as they are in contact with the soil (in the fall), then send up the leaf shoot in the spring.
Acorns are too heavy forwind dispersal, so they require other ways to spread. Oaks therefore depend onbiological seed dispersal agents to move the acorns beyond the mother tree and into a suitable area for germination (including access to adequate water, sunlight and soil nutrients), ideally a minimum of 20–30 m (70–100 ft) from the parent tree.[citation needed]
Many animals eat unripe acorns on the tree or ripe acorns from the ground, with no reproductive benefit to the oak, but some animals, such assquirrels andjays serve as seed dispersal agents. Jays and squirrels that scatter-hoard acorns in caches for future use effectively plant acorns in a variety of locations in which it is possible for them to germinate and thrive.
Even though jays and squirrels retain remarkably large mental maps of cache locations and return to consume them, the odd acorn may be lost, or a jay or squirrel may die before consuming all of its stores. A small number of acorns manage to germinate and survive, producing the next generation of oaks.
Scatter-hoarding behavior depends on jays and squirrels associating with plants that provide good packets of food that are nutritionally valuable, but not too big for the dispersal agent to handle. The beak sizes of jays determine how large acorns may get before jays ignore them.
Acorns germinate on different schedules, depending on their place in the oak family. Once acorns sprout, they are less nutritious, as the seed tissue converts to the indigestiblelignins that form the root.[20]
Water with acorn boiling in a pot, Kimotong, South Sudan
In some cultures, acorns once constituted a dietarystaple, though they have largely been replaced bygrains and are now typically considered a relatively unimportant food, except in some Native American and Korean communities.
Several cultures have devised traditional acorn-leaching methods, sometimes involving specialized tools, that were traditionally passed on to their children by word of mouth.[23][24]
Acorns served an important role in early human history and were a source of food for many cultures around the world.[25]Dental microwear suggests thatNeanderthals in Belgium consumed acorns among other hard foods.[26] Many modern human cultures relied on acorns,[25] such as theAncient Greek lower classes and the Japanese (during theJōmon period), for instance.[27] In antiquity,Pliny the Elder noted that acorn flour could be used to make bread.[28]
Acorns rarely form a large part of modern diets and are not currently cultivated on scales approaching that of many other nuts. However, if properly prepared (by selecting high-quality specimens andleaching out the bitter tannins in water), acorn meal can be used in some recipes calling for grain flours. Varieties of oak differ in the amount of tannin in their acorns. Varieties preferred by Native Americans, such asQuercus kelloggii (California black oak), may be easier to prepare or more palatable.[29]
Roasted acorn flour is a main ingredient in sweet cakes special toKurdish areas ofIran andIraq.[30][31]
Acorns are a traditional food of manyindigenous peoples of North America, and long served an especially important role forCalifornian Native Americans, where the ranges of several species of oaks overlap, increasing the reliability of the resource.[32] One ecology researcher ofYurok andKaruk heritage reports that "his traditional acorn preparation is a simple soup, cooked with hot stones directly in a basket," and says he enjoys acorns eaten with "grilledsalmon,huckleberries orseaweed."[33]
In theSan Francisco Bay Area acorns found were often associated with grinding tools.Stone tools like hammerstone and anvil, millingstones, andmortar and pestle help crack open the acorn and grind the acorn into dust.[34]
^Barrett, Reginald H. (1980)."Mammals of California Oak Habitats-Management Implications"(PDF). In Plumb, Timothy R. (ed.).Proceedings of the symposium on the ecology, management, and utilization of California oaks, June 26–28. USDA Forest Service General Technical Report PSW-044. pp. 276–291.
^abBarringer, Sam."Acorns Can be Deadly".West Virginia University Extension Service. Archived fromthe original on 27 February 2014. Retrieved27 January 2014.
^Brown, Leland R. (1979)Insects Feeding on California Oak TreesinProceedings of the Symposium on Multiple-Use Management of California's Hardwood Resources, Timothy Plum and Norman Pillsbury (eds.).
^Alphonso, Christina (5 November 2015)."Acres of Acorns".The Metropolitan Museum of Art, i.e. The Met Museum. Retrieved15 April 2017.
^Derby, Jeanine A. (1980)."Acorns-Food for Modern Man"(PDF). In Plumb, Timothy R. (ed.).Proceedings of the symposium on the ecology, management, and utilization of California oaks, June 26–28. USDA Forest Service General Technical Report PSW-044. pp. 360–361.
^Suttles, Wayne (1964), "(Review of) Ecological Determinants of Aboriginal California Populations, by Martin A. Baumhoff",American Anthropologist, vol. 66, no. 3, p. 676,doi:10.1525/aa.1964.66.3.02a00360
^Buonasera, T.Y. (2013). More than acorns and small seeds: A diachronic analysis of mortuary-associated ground stone from the south San Francisco Bay area. Journal of Anthropological Archaeology, 32(2), 190–211.https://doi.org/10.1016/j.jaa.2013.01.003
^"Chikamauga and Chattanooga". Frequently Asked Questions. U.S. Forest Service. 27 October 2022. Retrieved27 October 2022.
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