Acorn

For other uses, see Acorn (disambiguation).

Acorns of Sessile Oak

The acorn, or oak nut, is the nut of the oaks and their close relatives (genera Quercus and Lithocarpus, in the family Fagaceae). It usually contains a single seed (rarely two seeds), enclosed in a tough, leathery shell, and borne in a cup-shaped cupule. Acorns vary from 1–6 cm long and 0.8–4 cm broad. Acorns take between about 6 and 24 months (depending on the species) to mature; see List of Quercus species for details of oak classification, in which acorn morphology and phenology are important factors.

Ecological role

A group of acorns on a branch

Acorns play an important role in forest ecology when oaks are the dominant species or are plentiful. The volume of the acorn crop may vary wildly, 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 termed mast.

Wildlife which eat acorns as an important part of their diets include birds, such as jays, pigeons, some ducks, and several species of woodpeckers. Small mammals that feed on acorns include mice, squirrels and several other rodents.

Large mammals, such as pigs, bears, and deer, also consume large amounts of acorns; they may constitute up to 25% of the diet of deer in the autumn. In Spain and Portugal, pigs are still turned loose in dehesas (large oak groves) in the autumn, to fill and fatten themselves on acorns. However, acorns are toxic to some other animals, such as horses.

The larvae of some moths and weevils also 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 of protein, carbohydrates and fats, as well as the minerals calcium, phosphorus and potassium, and the vitamin niacin. Total food energy in an acorn also varies by species, but all compare well with other wild foods and with other nuts.

Acorns also contain bitter tannins, the amount varying with the species. Since tannins, which are plant polyphenols, interfere with an animal's ability to metabolize protein, creatures must adapt in different ways to use the nutritional value acorns contain. Animals may preferentially select acorns that contain fewer tannins.

Animals that cache acorns, such as jays and squirrels, may wait to consume some of these acorns until sufficient groundwater has percolated through them to leach out the tannins. Other animals buffer their acorn diet with other foods. Many insects, birds, and mammals metabolize tannins with fewer ill effects as opposed to 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 red oaks. The acorns of white oaks, being much lower in tannins, are nutty in flavor, which 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 water no longer turns brown. Being rich in fat, acorn flour can spoil or get moldy 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.

Dispersal agents

Acorns are a vital food source for squirrels.

Ponies eating acorns

Acorns are too heavy for wind dispersal, so they require other ways to spread. Oaks therefore depend on biological 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 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 as squirrels and jays 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 indigestible lignins that form the root.

Cultural relevance

In some human cultures, acorns once constituted a dietary staple, though they are now generally considered a minor food with the exception of Native American and Korean cultures.

Several indigenous human cultures have devised traditional acorn-leaching methods that involved tools and that were traditionally passed on to their children by word of mouth.

Mythology

The Norse legend that Thor sheltered from a thunderstorm under an oak tree has led to the belief that having an acorn on a windowsill will prevent a house from being struck by lightning, hence the popularity of window blind pulls decorated as acorns.

As food

Acorns served an important role in early human history and were a source of food for many cultures around the world. For instance, the poorer Ancient Greeks would eat acorns in their food and in the Jōmon period of Japan, acorns were harvested, peeled and soaked in natural or artificial ponds for several days to remove tannins, then processed to make acorn cakes.^{[citation needed]} In ancient Iberia they were a staple food, according to Strabo. Despite this history, acorn is currently not a significant source of calories for modern societies. Mush made with acorn meal is bland and unappetizing to modern tastes. However, if properly prepared by selecting fresh, or frozen, acorns that are not infested by insects; hulling and peeling them; grinding them, leaching out the colored tannin in fresh running water, or hot water; then using the meal or drying it for later use, acorn meal may be used in many recipes as a substitute for flour or other ingredients. Generally only a half or a third of the amount of the original ingredient should be replaced with acorn meal. Leaching acorn meal or flour requires a cloth bag or other filter. Varieties of oak vary in the amount of tannin in their acorns. Varieties preferred by American Indians such as Quercus kelloggii (California black oak) may be easier to prepare or more palatable.

Dotorimuk muchim (도토리묵무침), a Korean dish made with acorn starch

In Korea, an edible jelly named dotorimuk is made from acorns, and dotori guksu are 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.^{[citation needed]}

In Germany, acorns were one of several ingredients of Ersatz coffee during the Second World War.

Use and management by Native Americans

 

Mortar holes for pounding acorns into flour, Lost Lake, California

Acorns were a traditional food of many indigenous peoples of North America, but served an especially important role for Californian Native Americans, where the ranges of several species of oaks overlap, increasing the reliability of the resource.

Unlike many other plant foods, acorns do not need to be eaten or processed right away, but may be stored for a long time, as done by squirrels. 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 them in the sun to discourage mold and germination, women took acorns back to their villages and cached them in hollow trees or structures on poles, to keep them safe from mice and squirrels. The stored acorns could then be used when needed, particularly during the winter when other resources were scarce. Those acorns that germinated in the fall were shelled and pulverized before those that germinate in spring. Because of their high fat content, stored acorns can become rancid. Molds may also grow on them.

Native North Americans took an active and sophisticated role in managing acorn resources by using fire, which increased the production of acorns and made them easier to collect.^{[citation needed]} The light ground fires killed the larvae of acorn moths and acorn weevils by 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 open oak savannas with trees ideally spaced to maximize acorn production.

In art

A motif in Roman architecture and popular in Celtic and Scandinavian art, the symbol is used as an ornament on cutlery, jewelry, furniture, and appears on finials at Westminster Abbey. The Gothic name akran had the sense of "fruit of the unenclosed land". 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, popular etymology connected the word both with "corn" and "oak-horn", and the spelling changed accordingly.

Contemporary use as symbol

Acorn waymark for National Trails

The acorn is the symbol for the National Trails of England and Wales, and is used for the waymarks on these paths. The acorn, specifically that of the white oak, is also present in the symbol for the University of Connecticut.

See also

• Knopper gall

External links and further reading

• Nupa Acorn Soup (Miwokan recipe)
• Cooking With Acorns: A Major North American Indian Food
• Krautwurst, Terry (September/October 1988). "A Fall Field Guide Nuts". Mother Earth News. http://www.motherearthnews.com/Nature-Community/1988-09-01/A-Fall-Field-Guide-to-Nuts.aspx. Retrieved 20 October 2009. 
• Julia F. Parker and Beverly R. Ortiz, It Will Live Forever: Traditional Yosemite Indian Acorn Preparation, Heyday Books, 2nd revised edition (September 1, 1996), trade paperback, 160 pages, ISBN-10: 0930588452, ISBN-13: 978-0930588458
• Proceedings of the symposium on the ecology, management, and utilization of California oaks, June 26-28] USDA Forest Service General Technical Report PSW-044, Berkeley, California, 1980, edited by Timothy R. Plumb, 368 pages

  The symposium, held at Scripps College in Southern California, addressed most aspects of California's vast oak resource. Papers represented four major subject categories: ecological relationships, silviculture and management, damage factors, and products. Both scientific and applied information was presented, including original material not published previously. Individual topics ranged from taxonomy and historical relationships to management of insects and diseases. and various oak products. In California. oaks' value for wildlife, recreation, watershed protection, and esthetics exceeds their value for traditional lumber and wood products.

 This article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). Encyclopædia Britannica (11th ed.). Cambridge University Press.