Quercus undulata Torrey grisea (Liebm.) Engelm.
Quercus grisea is a deciduous or semi-evergreen large, multi-stemmed shrub or medium-sized, usually single-stemmed tree; it can grow up to 10 metres tall, exceptionally to 20 metres with a bole 180cm in diameter[
]. Shrubby forms growing in difficult situations can be less than 45cm tall, often spreading at the roots to form a thicket[
The plant is harvested from the wild for local use of its wood, and probably also as a food and a medicine. It is sometimes grown as an ornamental.
All parts of the plant contain tannins. Whilst tannins are found in many foods, and have a range of medicinal uses. They are usually only present in low concentrations. In some foods made from oaks (particularly the seeds), the tannin content can be quite high unless the food is treated to reduce tannin content.
Tannins are only of low toxicity and, because of their bitter taste and astringency, are unlikely to be eaten in large quantities. However, if they are taken in excess, they can cause stomach pains; constipation followed by bloody diarrhoea: excessive thirst; and excessive urination[
Southern N. America - Arizonia, New Mexico, Texas, northern Mexico
Igneous or dolomitic slopes, oak woodlands, juniper woodlands, desert chaparral; usually at elevations above 1,500 metres[
]. Found along drainages, arroyos, on rocky slopes, foothills, bajadas, stream sides, and terraces[
|Other Uses Rating||
|Cultivation Status||Ornamental, Wild
Quercus grisea occurs in semiarid climates characterized by mild winters, hot summers, and dry springs[
]. It is a fairly cold-hardy tree, tolerating temperatures down to around -20°c when dormant. It grows best in areas with hot summers, however. In areas with cooler summers, such as the maritime regions of the temperate zone, it often grows poorly, failing to properly ripen its wood and suffering frost damage over the winter[
Requires a sunny position[
]. Prefers an acidic soil, though can tolerate a pH to 6.9[
]. It is found in the wild on shallow, rocky soils with textures that range from clays to sandy loams. The soils often are derived from igneous or dolomitic parent materials[
The tree resprouts from the base if cut down or top-killed by fire[
The tree has a low-growing form in open savannahs, reaching tree size when growing in mesic canyons[
Numerous hybrids between Quercus grisea and other white oaks, including Quercus gambelii , Quercus mohriana , Quercus arizonica , and numerous species in northern Mexico, have been reported. In the Hueco and Quitman mountains of trans-Pecos Texas, putative hybrids of Quercus grisea × Quercus turbinella Greene occur[
The light brown, ovoid to narrowly ovoid or ellipsoid seed is 12 - 18mm long and 8 - 12mm wide[
]. Although no direct reference of edibility has been seen, this species belongs to the white oak subgenus, where the seeds are generally low in tannins and are often eaten[
The seed is usually cooked before eating, though it can also be eaten raw. It can be eaten whole, though it is more commonly dried, then ground into a powder and used as a thickening in stews etc or mixed with cereals for making bread.
In some species, especially many of those classified as 'white oaks', the seeds are low in tannins and have a more or less sweet and agreeable flavour. The seed of most species, however, have a very bitter flavour, due especially to the presence of tannins. In these species there are various processes that can remove or at least reduce the amount of these bitter substances (although other water-soluble substances, including some minerals, will also be removed).
Tannins are water-soluble and therefore the easiest way to remove or reduce tannin levels is by soaking in water. A few different methods are listed:-
A traditional method of preparing the seed was to bury it in boggy ground overwinter and allow the wet soil to gradually leach the tannins. The germinating seed was dug up in the spring when it would have lost most of its astringency and bitterness.
Another method was to wrap the seeds in a cloth bag and place them in a stream for several weeks.
Drying the seed and grinding it to a powder before soaking speeds up the process. The fastest method is to use hot water, by cooking the powder and changing the water several times until the cooking water is no longer bitter. Alternatively, you can use cold water (which is reported to produce the best quality flour). In this case, you soak the powdered seed in cold water for 12 - 24 hours then discard the water. Repeat this process for a number of times until the soak water is no longer bitter.
The roasted seed of many Quercus species has been used as a coffee substitute.
Quercus (oak) species are used in the traditional medicine of many cultures, being valued especially for their tannins. Various parts of the plant can be used, most frequently it is the leaves, bark, seeds, seed cups or the galls that are produced as a result of insect damage. A decoction or infusion is astringent, antibacterial, antifungal, antiseptic, styptic and haemostatic. It is taken internally to treat conditions such as acute diarrhea, dysentery and haemorrhages. Externally, it is used as a mouthwash to treat toothache or gum problems and is applied topically as a wash on cuts, burns, various skin problems, haemorrhoids and oral, genital and anal mucosa inflammation[
]. Extracts of the plant can be added to ointments and used for the healing of cuts[
The leaves of most species in this genus are more or less rich in tannins. A mulch of the partially decayed leaves can be placed around vulnerable plants in order to repel slugs, snails, grubs etc, and these will in time break down to add humus and nutrients to the soil. Fresh leaves should be used with caution, however, since as these decay they utilize some of the nitrogen in the soil and thus can inhibit plant growth[
Oak galls are excrescences that are sometimes produced in great numbers on the tree and are caused by the activity of the larvae of different insects. The insects live inside these galls, obtaining their nutrient therein. When the insect pupates and leaves, the gall can be used as a rich source of tannin, that can also be used as a dyestuff and is also used by many cultures to make ink[
The bark of oak trees is also usually rich in tannins and can be used as a dyestuff and for waterproofing rope[
The wood is hard and heavy. Because of its usually small dimensions it has little commercial value, though it is used as fence posts and, when larger sizes become available, it is used to make furniture[
The wood is used for fuel[
Seed - it quickly loses viability if it is allowed to dry out. It can be stored moist and cool overwinter but is best sown as soon as it is ripe in an outdoor seed bed, though it must be protected from mice, squirrels etc. Small quantities of seed can be sown in deep pots in a cold frame. Plants produce a deep taproot and need to be planted out into their permanent positions as soon as possible, in fact seed sown in situ will produce the best trees[
]. Trees should not be left in a nursery bed for more than 2 growing seasons without being moved or they will transplant very badly.