(Editor's Note: This article was originally published on October 12, 2009. Your comments are welcome, but please be aware that authors of previously published articles may not be able to respond to your questions.)

The acorn may be small, but it holds a world inside. The nut consists of three parts: the cup (or cupule), a tough outer shell, and a kernel. The acorn’s cup is probably the most fascinating part to children, as it resembles nothing so much as a tiny brown hat. It may be shallow, or may almost completely enclose the nut. Some acorn cups can be rough and prickly, while others have smooth scales. The kernel is made up of two fat-rich seed leaves called cotyledons which enclose a tiny embryo at the pointed end of the nut. The nuts themselves vary in shape from round to tapered, with a size ranging from 1/2 to 1 1/2 inches in length. The color of the acorn may be green, yellow, brown or any shade in between.

"The creation of a thousand forests is in one acorn” -- Ralph Waldo Emerson

The tree that produces the acorn is the oak, whose Latin name “Quercus” is thought to be derived from a Celtic word meaning “fine tree”. Oak trees can live to 200 years or more. Until a 2002 storm took it down, the largest oak tree on record was the famous Wye Oak in Wye Mills, Maryland. With a 31 feet, 10 inch circumference and a crown spread of 119 feet, it was believed to be over 460 years old at the time of its destruction. An oak must reach at least 20 years, sometimes as much as 50 years, before it bears acorns. By the time an oak tree is 70 to 80 years old, it will produce thousands of acorns. An oak tree may not produce acorns every single year; after a year with heavy production the tree may produce only a light crop or no crop at all in the following year. In 2004, the oak tree was officially recognized as the national tree of the United States.

The appearance of the acorn is dependent on the type of oak which produces it. There are more than 60 species in the United States alone. The two major classes of oak are the white oak, which has rounded leaf lobes, and the red oak, which has pointed spine-tipped leaf lobes. Depending on the species, acorns take about 6 or 24 month to mature. White oak acorns don’t last long because they grow and fall in just a few months, whereas red oak acorns take a full two years to ripen. Acorns of the white oaks are quick to decay and are sweet to the taste and likely to be gobbled up quickly by wildlife. You are much more likely to find red oak acorns on the ground, not only because they are more resistant to decay, but because their high tannin content makes them less attractive to wildlife. While squirrels eat white oak acorns right away, they tend to bury the more bitter red oak nuts for later. Over time, moisture in the ground helps leach out the tannins, making the nut more palatable.

Identifying Leaves and Acorns of the Two Major Oak Classes

White Oak Leaves
between 5 to 9 rounded leaf lobes
no bristle at the tip

Red Oak Leaves
between 7 to 9 pointed, spine-tipped leaf lobes
leaf tip has pointy bristle

White Oak Acorns
• inner surface of cap always hairless
• scales on cap usually fleshy
• mature and fall from the tree same year they are formed
• low concentration of tannin
• germinate in the same year in which they fall

Red Oak Acorns
• inner surface of cap always hairy
• scales on cap usually flat and overlapping

• mature in their second year
• high concentration of tannin
• germinate the spring after they fall

"From little acorns mighty oaks do grow” -- American proverb

Because acorns are too heavy to travel very far from their parent tree, the oak is dependent on animals such as birds and squirrels to disperse its seed. According to one source, the odds of one acorn actually growing into an oak tree are very small--less than 1 in 10,000.[1] Acorns contain large amounts of protein, carbohydrates and fat, making them a favored food of many animals. Though squirrels are the first creatures who come to mind as acorn consumers, many other animals relish this nut, including mice, jays, pigeons, woodpeckers, and even large mammals such as deer, pigs and bears. In the dense oak forests of southwest Europe, farmers still turn their pigs loose in the autumn to fatten on acorns. Acorns are toxic to some other animals, however, including horses. Acorns have also been used as food by humans in many cultures. In ancient Japan, acorns were soaked in river water to removed the tannins, then made into acorn cakes. In Korea, acorns are used to make a jelly called “dotorimuk”. Acorns were a traditional food of Native Americans, who ground the nutmeats to prepare flour.

"Faith sees a beautiful blossom in a bulb, a lovely garden in a seed, and a giant oak in an acorn.” -- William Arthur Ward

ImageAcorns frequently appear as a symbol in folklore and a motif in art. Acorn designs can be found on jewelry, furniture and architecture dating back centuries. Acorns served as a talisman to ancient Druids and Romans. The Roman goddess Diana is frequently depicted wearing a necklace of acorns. In Nordic legend, Thor, the god of thunder, sought safety under an oak tree during a storm. In Scandinavian countries it was believed that putting an acorn on a sill would protect a home from lightning. You can still find this ancient belief reflected in window blind pulls, which have historically been made in the shape of acorns.

Acorns are a common theme in folklore. The oak was considered the king of the forest and was supposed to harbor fairies, who wore the tops of the acorns as hats. It was said that a young woman could foretell her future by naming two acorn cups for herself and her sweetheart, then floating them in a bowl of water. If the cups sailed together, a marriage would follow; if they sailed apart, separation would ensue. A German folktale tells of a farmer who has promised his soul to Satan, but asks for a reprieve until his first crop is harvested. The devil grants it, but the farmer outwits him by planting acorns, thus ensuring himself a long life.

Another old folk belief is that carrying an acorn brings the wearer good fortune, and can even prevent his or her aging. Still another claims that if you plant an acorn on a moonless night you will receive money in the near future. So, the next time you walk beneath an oak tree, pocket a few of those acorns. They will serve as a reminder of the power contained in a tiny nutshell, of the importance of perseverance in achieving your goals, and of the strength, fortitude and grandeur of the oak tree. And as if that's not enough, they just might bring you good luck!

Read Sharon Brown's article for information about the White Oak.

Read Kelli Kallenborn’s article on balanophagy, the practice of eating acorns.

Footnotes: [1] Interesting Facts About Acorns

Photo credits: "Acorn" thumbnail by randihausken; "Acorns and Caps on Ground" by Martin LaBar

Other sources:
The Acorn: History of Superstitions
When Nature Goes Nuts