Fagaceae

Beech Family

Oaks

FAMILY: Beech family (Fagaceae) – Quercus genus.

SPECIES: All oaks (Quercus) produce edible acorns. Note that poison oaks (Toxicodendron) are unrelated and produce berry-like fruits rather than acorns. #1 Arizona white oak (Quercus arizonica Sarg.). #2 golden-cup oak or canyon live oak (Quercus chrysolepis Liebm.). #3 Emory’s oak (Quercus emoryi Torr.). #4 Gambel’s oak (Quercus gambelii Nutt.). #5 gray oak (Quercus grisea Liebm.). #6 silverleaf oak (Quercus hypoleucoides A. Camus). #7 Mexican blue oak (Quercus oblongifolia Torr.). #8 Palmer’s oak (Quercus palmeri Engelm. = Quercus dunnii Kellogg). #9 pungent or sandpaper oak (Quercus pungens Liebm.). #10 netleaf oak (Quercus rugosa Née = Quercus reticulata Engelm.). #11 turbinella, scrub, or shrub live oak (Quercus turbinella Greene).

TO UTILIZE AS FOOD: Warning! Consuming raw acorns can cause digestive upset, abdominal pain, vomiting, diarrhea, internal bleeding, kidney damage, or damage to the intestinal tract. Raw acorns contain excessive amounts of tannins that need to be removed. Tannins are a diverse group of complex compounds that are widespread in the plant kingdom. In small amounts, they offer many health benefits. In large amounts, they are toxic. In plants they serve as defensive compounds against grazing animals, insects, microorganisms, and diseases. As a group, they are bitter, astringent, water-soluble compounds that have the ability to bind proteins and deactivate enzymes, which promptly brings cell functions to a halt. Their ability to bind proteins makes them useful for turning animal hides into leather. “Tanna” is an old German word for oaks. Even the best-quality acorns usually need to be processed to remove the tannins.

All oak shrubs and trees produce edible acorns (Angier pp. 24-25 and Kirk pp. 104-106), but some acorns taste much better than others. Acorns were a primary component of the ancestral diet and are still harvested to this day. Considering the extent to which acorns have been utilized as food, it’s reasonable to conclude that the various processing techniques effectively remove the tannins and render them safe, which should alleviate any concerns over toxicity. About 600-700 species of oaks occur on Earth, primarily in the northern hemisphere. Cells of oak shrubs/trees store tannins within tiny compartments called vacuoles. Breaking the cells releases the tannins. This occurs when animals eat the various parts of oaks or when the cells are damaged by other factors. Acorns must be shelled, ground, and leached. Soaking coarsely ground nutmeat in water effectively leaches the tannins. Traditionally, acorns were leached in a cool stream for several days. Modern methods such as boiling are also effective and more expedient. A percentage of carbohydrates are lost in the process, but most of the fats and proteins endure. Acorn nutmeat has a wide range of dull colors. Lighter-colored nutmeat is generally better than darker-colored nutmeat. Raw nutmeat is excessively bitter, but it usually tastes good after processing. Processed acorns are nutritious, but most other nuts are considerably more nutritious. All species discussed below produce acorns sometime from midsummer to late autumn. Elevation influences the harvest time and most of these species have a preferred elevation, usually between 1,200 and 2,700 meters (about 3,500 to 8,000 feet). All these species are native to the southwestern United States, so they’re well adapted to the region. Their acorns mature in one year, except for those of golden cup oak (Q. chrysolepis) and Palmer’s oak (Q. palmeri) which require two years to mature. Oaks are often subdivided into groups based on acorn features, leaf features, how long the acorns require to mature, and other details. Those last two species are part of a “golden oaks” group, which isn’t always recognized. Acorns of the “white oaks” group generally taste better than those of the “red oaks” group. Only 2 representatives of the red oaks group, silverleaf oak (Q. hypoleucoides) and Emory’s oak (Q. emoryi), occur in the Southwest. Some authorities place them in a “black oaks” group. As with most members of the red oaks group, their inner acorn shells are hairy, but unlike most red oaks their acorns mature in only one year. Except for these 2 golden oaks and 2 red oaks, all species listed above are white oaks. The following notes are based on 7 of those 11 species, 4 species eluded my efforts.

Arizona white oak (Q. arizonica) produces acorns essentially identical to those of netleaf oak described below. These species only differ by length of pedicels. Fresh nutmeat is white with a yellowish tinge. Shells are dark brown, shiny, and hairless. The nuts are relatively low in tannins. Fallen acorns remain available for a short period of time. Weather patterns and hungry animals determine how long this period lasts. If the weather is dry, acorns dehydrate and remain usable for several weeks, or possibly for several months. If the weather is wet, acorns may sprout or rot. Arizona white oak is found primarily in southern Arizona and southern New Mexico.

Golden-cup oak (Q. chrysolepis) is found primarily in California and Arizona. Some authorities consider it part of a “golden oaks” group for the golden hairs on the leaves and cups. Acorns of this species require two years to mature. It’s a fairly common species, but the acorns were not sampled for this reference. William Sturtevant (1978 p. 374) indicates that the acorns of this species were among those preferred by the Konkow Indians of northern California. Many other native people of California utilized golden-cup acorns as a primary food item.

Emory oak (Q. emoryi) produces decent acorns. Fresh nutmeat is yellowish and relatively sweet by acorn standards. Plenty of astringency is also present, along with carbohydrates and yeast-like overtones. One leaching usually suffices to render the nutmeat palatable. Emory oak acorns are small. What they lack in size they make up in flavor. Gambel oak acorns taste superior, but not by much. Emory oak acorns taste odd, bitter, and bread-like. It’s a rather strong flavor and it’s not like hazelnuts. Sweetness is prevalent, but it’s overrun by less appealing aspects. Emory oaks and silverleaf oaks share similarities in flavor, yet maintain individuality. Both species have hairy acorn skins and belong to the “red oaks” group. Most southwestern oaks belong to the “white oaks” group. Differences in acorn flavor between these groups are clearly evident. Emory oaks are common in Arizona and New Mexico.

Gambel oak (Q. gambelii) produces high-quality acorns that represent the gold standard of acorns in the Southwest. Some acorns may taste good enough to eat raw, but the majority of them taste bitter due to the presence of tannins. After processing, the flavor is similar to hazelnuts. As acorns mature, the shells turn from green to brown. Inside each shell is a white nut with a crispy texture. Fresh acorn nutmeat is moist and quickly rots unless kept in a cool place where it can breathe. Long-term storage requires dehydration. Cracking the shells by hand allows for careful inspection of the nutmeat for signs of infestation. Acorns tend to be wormy and moldy. Even the healthiest oak trees are rarely free of infestation. Shells and nutmeat cannot be separated with water because they both sink. Smashing the acorns with a rock and sifting the mess to remove the shells has limited effectiveness. Old-fashioned hand separation is apparently the best technique for obtaining pure nutmeat free of shells. After the chore of shelling, chunks of raw nutmeat can be pounded into a coarse meal, boiled to remove the tannins, dehydrated, and then toasted to bring out the elusive nutty flavor. This ready-to-eat meal was a staple of life. Finely grinding the meal produces acorn flour. Early autumn is acorn season. Mature acorns readily fall to the ground, which usually occurs when the leaves turn rusty shades of red, orange, and yellow. Fallen acorns of the current season are fine to collect, but they mix with acorns from previous seasons that may be rotted. Differences aren’t always obvious until the acorns are shelled. Gambel oaks grow throughout the Southwest in mountain habitats around 2,000 meters elevation.

Gray oak (Q. grisea) produces sizable acorns of good quality that mature toward the end of summer. All aspects of the acorns are comparable to those of Gambel oak described above. Gray oak acorns have dark-brown shells and whitish nuts. Raw nutmeat is too astringent for consumption. After processing, the nutmeat is ideal for making pancakes, muffins, breads, and other goods. One change of water should suffice for leaching out the bitter tannins, and then dry roasting the soggy nutmeat will do a lot to bring out its nutty flavor. Dry roasting also drives out moisture and prepares the nutmeat for long-term storage. Gray oaks are common in Arizona and New Mexico.

Silverleaf oak (Q. hypoleucoides) produces average-quality acorns. Outer shells are often streaked with orange lines and covered with dusty powder. Inner shells and nut skins are densely hairy. Nutmeat normally has a yellowish-orange tint. Silverleaf acorns were not meant to be eaten fresh, perhaps not cooked either. The flavor isn’t too awful compared to acorns in general, but it’s definitely unappealing. Fresh acorns are moist and quickly rot unless kept in a cool place. Long-term storage requires dehydration. Fresh nutmeat has an odd, bitter, bread-like flavor with a yeast-like accent and minimal sweetness. It’s not a nutty flavor. Emory oaks are clearly related to silverleaf oaks. Both are members of the “red oaks” group. Silverleaf oaks are found primarily in southeastern Arizona and southwestern New Mexico.

Mexican blue oak (Q. oblongifolia) is found primarily from southern Arizona to southern New Mexico and southward into Mexico. It’s a dominant tree in the Atascosa and Pajarito mountains of Arizona, but it wasn’t very forthcoming with acorns during the fieldwork conducted for this reference. In contrast to other oaks in the area, leaves of Mexican blue oak have a definite bluish cast, so the name is well chosen. Acorns of this species were a staple food item and article of trade for the Tohono O’odham (Papago) Indians. Daniel Austin (p. 151) notes that many sources consider the acorns to be of good quality.

Palmer’s oak (Q. palmeri) is closely related to golden-cup oak, but its usage among Native Americans appears to be infrequent. During the fieldwork conducted for this reference, colonies of Palmer’s oak were located in the Mazatzal Mountains of central Arizona, but acorn production was not sufficient enough to merit documentation.

Sandpaper or pungent oak (Q. pungens) grows from southeastern Arizona to southwestern Texas and southward into Mexico. It’s a shrubby species that was apparently of little or no value to Native Americans. The quality of its acorns is uncertain. Considering the lack of references to the utilization of sandpaper oak acorns, it’s unlikely that they are very palatable. However, Delena Tull (1999 p. 102) notes that acorns of a closely related species called Vasey’s oak (Q. vaseyana) are reported to be among the sweetest in Texas.

Netleaf oak (Q. rugosa) produces impressively large acorns of average quality that are available over a relatively long period of time. Flavor, texture, aroma, appearance, and other aspects are similar to those of Gambel oak acorns described above. Freshly shelled acorns range in color from light brown to light pink. Despite the light color, which is typically a sign of low tannin content, the acorns are loaded with tannins. Multiple changes of water are necessary to render the acorns palatable. After removing the tannins, the acorns can be mashed into nut butter. Dry roasting adds a nice accent. Netleaf oak is fairly common in the mountain ravines of southern Arizona and southern New Mexico, and southward into Mexico.

Shrub oak (Q. turbinella) produces low- to average-quality acorns. This species integrates with several other species, which is normal for oaks. Most aspects, except for flavor, are similar to Gambel oak acorns. Shrub oak acorns may taste inferior to those of other species, but they’re usually more abundant and less infested. Fresh nutmeat is creamy white. Bitterness is hard to subdue even after multiple changes of cooking water. Three changes of water followed by drying and roasting produces a fair-quality flour, so harvesting and processing the acorns is ultimately worth the effort. Spiny leaves present a serious hazard, so gloves are recommended when harvesting this resource. Shrub oak is abundant on marginal lands nearly throughout the Southwest.

NOTES: Acorn production varies seasonally. Even the healthiest oaks rarely produce a good crop two years in a row. Oaks bloom early, so the flowers are susceptible to late season frosts. Freezing temperatures that kill the flowers in spring prevent acorns from developing later in autumn. One late season frost can devastate acorn production for hundreds of miles. Droughts, insects, and molds can also devastate the harvest. Loss can be near total. Productive trees can be difficult to find. Acorn weevils bore tiny holes into acorns to lay eggs. The developing larvae feed upon the nutmeat and mature in autumn. Boring holes are clearly visible, but acorns without holes may also be infested. The weevils cause significant losses. Infested acorns temporarily float in water since they’re filled with air, while healthy acorns sink.

A 100 gram serving of dried acorn nutmeat (species unspecified) contains: 509 kilocalories, 5.06 g water, 8.1 g protein, 31.41 g fat, 53.66 g carbohydrates, 1.78 g ash, 54 mg calcium, 103 mg phosphorus, 82 mg magnesium, 0 mg sodium, 709 mg potassium, 1.04 mg iron, 0.818 mg copper, 0.67 mg zinc, 1.363 mg manganese, various B vitamins, and other nutrients. Fatty acid profile: 4.084 g saturated fatty acids, 19.896 g monounsaturated fatty acids, 6,052 g polyunsaturated fatty acids. Source: USDA National Nutrient Database for Standard Reference.

IDENTIFICATION: Depending upon the reference, anywhere from 60 to 140 species of the Quercus genus are found in the United States. Many of these are hybrids. Only about 15 species are found in the Southwest. Acorns are the defining feature of the genus. Nothing else produces similar fruit structures. All the species are monoecious, meaning they have male and female flowers separate, but on the same shrub or tree. Therefore, acorns can potentially be found on any individual. Species are differentiated according to overall form, lifespan, leaves, hairs, acorns, and other features. Oaks are divided into two main groups: white oaks (Lepidobalanus) and red oaks (Erythrobalanus). Three additional groups (black, gray, and golden) share traits similar to the red group. White oaks have acorns that mature in 1 year, and red oaks have acorns that mature in 2 years (with a few exceptions). Other traits are inconsistent.

Description of oaks (the Quercus genus): FORM shrubs or trees; evergreen or deciduous; monoecious; LEAVES simple; alternate; blades entire, toothed, or lobed; surfaces hairless or variously hairy; FLOWERS unisexual; MALE flowers arranged in slender clusters that hang downward; calyces 4-6 lobed; petals absent; stamens 4-12; FEMALE flowers solitary or 2-3 in axillary clusters; each enclosed by an involucre of scaly bracts; ovary inferior; calyces usually 6-lobed; petals absent; styles 3-branched; FRUITS each acorn consisting of one nut enclosed by a shell, these loosely secured in scaly cup-like involucres; inner shells hairy or more often hairless; HABITAT preferring mid elevations (1,000 to 2,500 meters or about 3,000 to 8,000 feet), often forming thickets; blooming in spring.

REFERENCES: Angier (pp. 24-25) and Kirk (pp. 104-106) state that all oaks produce edible acorns. #1 Arizona white oak (Quercus arizonica): acorns Ebeling (p. 819). #2 canyon live oak (Quercus chrysolepis): acorns Ebeling (p. 819). #3 Emory’s oak (Quercus emoryi): acorns Ebeling (p. 819). #4 Gambel’s oak (Quercus gambelii): acorns Ebeling (p. 819) and many others. #5 gray oak (Quercus grisea): acorns Ebeling (p. 819). #6 silverleaf oak (Quercus hypoleucoides): acorns Ebeling (p. 819). #7 Mexican blue oak (Quercus oblongifolia): acorns Austin (pp. 150-152) and Ebeling (p. 819). #8 Palmer’s oak (Quercus palmeri = Quercus dunnii): acorns Moerman (p. 207). #9 sandpaper oak (Quercus pungens): acorns Standley (1922 p. 172) and Ebeling (p. 819). #10 netleaf oak (Quercus rugosa = Quercus reticulata): acorns Ebeling (p. 819). #11 shrub oak (Quercus turbinella): acorns Ebeling (p. 820). References to toxicity: Spoerke (pp. 55-58), Turner (1991 pp. 83-84), Tull (2013 p. 99), and Wesson (p. 3).