Acorn

This article is about the nut. For the squash, seeAcorn squash.For other uses, seeAcorn (disambiguation).

Theacornis thenutof theoaksand their close relatives (generaQuercusandLithocarpus,in the familyFagaceae). It usually contains aseedlingsurrounded by twocotyledons(seedling leaves), enclosed in a toughshellknown as the pericarp, and borne in a cup-shapedcupule.Acorns are1–6 cm (1⁄2–2+1⁄2in) long and0.8–4 cm (3⁄8–1+5⁄8in) on the fat side. Acorns take between 5 and 24 months (depending on the species) to mature; see thelist ofQuercusspeciesfor details of oak classification, in which acornmorphologyandphenologyare important factors.

English oakacorn

Acorns 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.)CupuleB.)Pericarp(fruit wall) C.) Seed coat (testa) D.)Cotyledons(2) E.)PlumuleF.)RadicleG.) Remains ofstyle.Together D., E., and F. make up the embryo.

Etymology

The wordacorn(earlierakerne,andacharn) is related to theGothicnameakran,which had the sense of "fruit of the unenclosed land".The word was applied to the most important forest produce, that of the oak.Chaucerspoke of "achornes of okes" in the 14th century. By degrees, popularetymologyconnected the word both with "corn" and "oak-horn", and the spelling changed accordingly.The current spelling (emergedc. 15th–16thcentury) derives from association withac(Old English: "oak" ) +corn.

Ecology

Ponieseating acorns. Acorns can cause painful death inequines,especially if eaten in excess.

Sprouting acorn ofQuercus robur

Acorns play an important role inforest ecologywhen oaks are plentiful or dominant in the landscape.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.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.Smallmammalsthat feed on acorns includemice,squirrelsand several otherrodents.One beetle species,Thorectes lusitanicus,also feeds on acorns.Acorns have a large influence on smallrodentsin theirhabitats,as large acorn yields help rodent populations to grow.

Large mammals such as pigs, bears, anddeeralso consume large amounts of acorns; they may constitute up to 25% of the diet of deer in the autumn.In Spain, Portugal and theNew Forestregion 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,especially if eaten in excess.

Thelarvaeof somemothsandweevilsalso live in young acorns, consuming the kernels as they develop.

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,carbohydratesandfats,as well as the mineralscalcium,phosphorusandpotassium,and thevitaminniacin.Totalfood energyin an acorn also varies by species, but all compare well with other wild foods and with other nuts.

Acorns also contain bittertannins,the amount varying with the species. Since tannins, which are plantpolyphenols,interfere with an animal's ability tometabolizeprotein, 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 causeulcerationandkidneyfailure.

Animals thatcacheacorns, such as jays and squirrels, may wait to consume some of these acorns until sufficient groundwater haspercolatedthrough them toleachout 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 oaksandEnglish 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.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.

Being rich in fat, acorn flour can spoil ormoldereasily 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.

Dispersal agents

Acorns are too heavy forwind dispersal,so they require other ways to spread. Oaks therefore depend onbiological seed dispersalagents 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.

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 assquirrelsandjaysserve 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 indigestibleligninsthat form the root.

Acorn, raw

Nutritional value per 100 g (3.5 oz)
Energy	1,619 kJ (387 kcal)
Carbohydrates	40.75 g
Fat	23.85 g
Saturated	3.102 g
Monounsaturated	15.109 g
Polyunsaturated	4.596 g
Protein	6.15 g
Tryptophan	0.074 g
Threonine	0.236 g
Isoleucine	0.285 g
Leucine	0.489 g
Lysine	0.384 g
Methionine	0.103 g
Cystine	0.109 g
Phenylalanine	0.269 g
Tyrosine	0.187 g
Valine	0.345 g
Arginine	0.473 g
Histidine	0.170 g
Alanine	0.350 g
Aspartic acid	0.635 g
Glutamic acid	0.986 g
Glycine	0.285 g
Proline	0.246 g
Serine	0.261 g
Vitamins and minerals Vitamins Quantity %DV† Vitamin A equiv. 0% 2 μg Thiamine (B1) 9% 0.112 mg Riboflavin (B2) 9% 0.118 mg Niacin (B3) 11% 1.827 mg Pantothenic acid (B5) 14% 0.715 mg Vitamin B6 31% 0.528 mg Folate (B9) 22% 87 μg Vitamin C 0% 0.0 mg Minerals Quantity %DV† Calcium 3% 41 mg Copper 69% .621 mg Iron 4% 0.79 mg Magnesium 15% 62 mg Manganese 58% 1.337 mg Phosphorus 6% 79 mg Potassium 18% 539 mg Sodium 0% 0 mg Zinc 5% 0.51 mg
Other constituents	Quantity
Water	27.9 g
Link to USDA Database entry
†Percentages estimated usingUS recommendationsfor adults,except for potassium, which is estimated based on expert recommendation fromthe National Academies.

Uses

In some cultures, acorns once constituted a dietarystaple,though they have largely been replaced bygrainsand 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.

Culinary

Acorns served an important role in early human history and were a source of food for many cultures around the world.For instance, theAncient Greeklower classes and the Japanese (during theJōmonperiod)would eat acorns, especially in times of famine.In ancientIberiathey were a staple food, according toStrabo.Despite this history, 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 andleachingout the bitter tannins in water), acorn meal can be used in some recipes calling for grain flours. In antiquity,Pliny the Eldernoted that acorn flour could be used to make bread.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.

In Korea, an edible jelly nameddotorimukis made from acorns, anddotori guksuare Korean noodles made from acorn flour or starch. In the 17th century, a juice extracted from acorns was administered to habitual drunkards to cure them of their condition or else to give them the strength to resist another bout of drinking.

Roasted acorn flour is a main ingredient in sweet cakes special toKurdishareas ofIranandIraq.

Acorns have frequently been used as acoffee substitute,particularly whencoffeewas unavailable or rationed. TheConfederatesin theAmerican Civil WarandGermansduringWorld War I(when it was calledErsatzcoffee), which were cut off from coffee supplies byUnionand Alliedblockadesrespectively, are particularly notable past instances of this use of acorns.

Use by Native Americans

Acorns are a traditional food of manyindigenouspeoples 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.One ecology researcher ofYurokandKarukheritage 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,huckleberriesorseaweed." Unlike many other plant foods, acorns do not need to be eaten or processed right away, but may be stored for a long time, much assquirrelsdo. In years that oaks produced many acorns, Native Americans sometimes collected enough acorns to store for two years as insurance against poor acorn production years.

After drying in the sun to discouragemouldandgermination,acorns could be cached in hollow trees or structures on poles to keep them safe from mice and squirrels. Stored acorns could then be used when needed, particularly during the winter when other resources were scarce. Acorns that germinated in the fall were shelled and pulverized before those germinating in spring.Because of their high fat content, stored acorns can become rancid. Moulds may also grow on them.

The lighting of ground fires killed the larvae ofacorn mothsandacorn weevilsby burning them during their dormancy period in the soil. The pests can infest and consume more than 95% of an oak's acorns.

Fires also released the nutrients bound in dead leaves and other plant debris into the soil, thus fertilizing oak trees while clearing the ground to make acorn collection easier. Most North American oaks tolerate light fires, especially when consistent burning has eliminated woody fuel accumulation around their trunks. Consistent burning encouraged oak growth at the expense of other trees less tolerant of fire, thus keeping oaks dominant in the landscapes.

Oaks produce more acorns when they are not too close to other oaks and thus competing with them for sunlight, water and soil nutrients. The fires tended to eliminate the more vulnerable young oaks and leave old oaks which created openoak savannaswith trees ideally spaced to maximize acorn production.

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  Mortar holesfor pounding acorns into flour,Lost Lake, California
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  Chuckachancywomen pause in their work preparing acorns for grinding, California,c. 1920

In culture

Campaign hat worn byGeneral Sherman

Art

AmotifinRoman architecture,also popular in Celtic and Scandinavian art, the acorn symbol is used as anornamentoncutlery,furniture, and jewelry; it also appears onfinialsatWestminster Abbey.

In theArtemis Fowlbook series, "The Ritual" describes the method used by faeries to regenerate their magical powers.

Military symbolism

The acorn was used frequently by bothUnionandConfederateforces during theAmerican Civil War.ModernUS ArmyCavalry Scoutcampaign hatsstill retain traces of the acorn today.

Contemporary use as symbol

The acorn is the symbol for theNational TrailsofEngland and Wales,and is used for thewaymarkson these paths.The acorn, specifically that of the white oak, is also present in the symbol for theUniversity of Connecticut.

Acorns are also used aschargesinheraldry.

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  Acorn waymark forNational Trailsin England and Wales
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  Acorn in the coat of arms of the du Quesne family
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  Oak branch with two acorns in the coat of arms ofTammela

See also

• Knopper gall

External links

• Media related toAcornsat Wikimedia Commons