In the northwest part of its range, Quercus macrocarpa varies clinally to smaller, shrubbier forms on bluffs and hillsides, with smaller, less fringed cups, that are the basis of Quercus macrocarpa var. depressa (Nuttall) Engelmann and Quercus mandanensis Rydberg. These scrubby forms may merit formal recognition after more thorough study; they are treated here as clinal variants of the species[].

Common Name: Burr Oak

General Information

Quercus macrocarpa is a deciduous tree with a dense, round, spreading crown; it usually grows up to 30 metres tall, though specimens up to 50 metres have been reported. The straight, cylindrical bole can be more than 200cm in diameter[, ]. On poor soil along the top of bluffs at the western edge of its range, it often forms dense thickets of low straggling shrubs which may be only 50 - 100cm tall[].
One of the best and most durable oak lumbers, Quercus macrocarpa is harvested from the wild on a commercial basis[]. The tree is also often harvested on a more local level as a food, medicine and source of materials. It makes an excellent ornamental for parks or other large areas[].
This species is noted for having the largest distribution of all the North American oak species. There are no known threats that would severely impact the survival of this species any time in the near future. The plant is classified as 'Least Concern' in the IUCN Red List of Threatened Species(2013)[].

Known Hazards

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[].

Botanical References

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Range

Central and eastern N. America - southern Saskatchewan to New Brunswick, south to Texas, Tennessee and Maryland

Habitat

Found in a variety of habitats from dry hillsides to moist bottomlands, rich woods and fertile slopes, mainly on limestone soils[, ].

Properties

Conservation Status	Least Concern
Edibility Rating
Medicinal Rating
Other Uses Rating
Habit	Deciduous Tree
Height	15.00 m
Growth Rate	Slow
Pollinators	Wind
Cultivation Status	Wild

Cultivation Details

Quercus macrocarpa is a very cold-hardy plant, tolerating temperatures down to about -35°c when dormant[]. It grows best in areas with hot summers. 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[, ]. A tree at the Hillier Arboretum in Hampshire, southern England was growing well in September 1993. It was 9 metres tall but had a lot of mildew, there was no sign of seeds[].
Grows best in a sunny position[], though young plants tolerate reasonable levels of side shade[]. Prefers a good deep fertile loam which can be on the stiff side[]. The tree is usually found in the wild on limestone or calcareous clay soils[]. Succeeds in a hot dry position. The plant endures a wide variety of harsh conditions including poor dry soils and wet, poorly drained, and inundated locations[]. Tolerates moderate exposure, surviving well but being somewhat stunted[]. A slow-growing tree[]. Established plants are drought resistant[] and tolerant of atmospheric pollution[].
Occasionally cultivated for its edible seed, there are some named varieties[].
The main sources of Quercus macrocarpa trees for timber are Iowa and Illinois bottomlands[].
The tree flowers on new growth produced in spring, the seed ripening in its first year[, ].
The large acorns are best developed in the southern part of the range, and a clinal decrease in acorn size and extent of the mossy fringe on the acorn cup seems to occur as one travels from south to north[].
It is a slow-growing but fairly long-lived species, reaching ages of 300 - 400 years old; some plants have been documented to reach up to 450 years of age[].
It takes about 30 years to start producing seed, though it then continues to crop for the next 200 - 300 years with large crops being produced every 2 - 3 years[].
This species is the state tree of Illinois[].
Hybridizes freely with other members of the genus[].
Putative hybrids with Quercus bicolor are common in the northeastern part of its range, where the two species often occur together in wet, poorly drained habitats. The effect of this contact may be partially responsible for morphologic differences across the range of Quercus macrocarpa[].
Trees have a thick, fire-resistant bark[].
There is a dwarf form of this species:- Quercus macrocarpa depressa (Nutt.)Engelm., grows about 2 metres tall with corky branches and smaller seeds than the species, usually about 10mm long[].
Plants in this genus are notably resistant to honey fungus[].

Edible Uses

Seed - cooked[, , , ]. The light brown or grayish, ovoid-ellipsoid or oblong seed can be 15 - 50mm long and 10 - 40mm wide[]]. The seed can be ground into a powder and used in making bread, dumplings etc and as a thickener in soups[]. The seed of this species is considered to be one of the most palatable of all the oaks[, ]. Many trees have sweet seeds with little tannin and the seed can be eaten raw or cooked.
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.

Medicinal

The bark is astringent and tonic[]. An infusion has been used in the treatment of diarrhoea[].

A decoction of the root or inner bark has been used in the treatment of cramps[].

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[, ].

Agroforestry Uses:

The tree has been widely tested for use in rehabilitation of the soil. It has been successfully planted on coal spoils in the north-central and northern Great Plains, and in the Western Interior Coal Province which encompasses Missouri, Kansas, and Oklahoma. It may be either seeded or transplanted onto disturbed areas[].

Other Uses

The leaves of most species in this genus are more or less rich in tannins. A mulch of the leaves can be placed around vulnerable plants in order to repel slugs, snails, grubs etc. Fresh leaves should be used with caution, since these can utilize some of the nitrogen in the soil and this 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[].

The bark has been used as a mordant for fixing dyes[].

The wood is hard, heavy, strong, tough, very durable, close grained. It weighs about 46lb per cubic metre[]. This species is of considerable importance as a timber tree, it is used for all types of construction, in making baskets, flooring, cabinet making, ship building, cooperagem fence posts etc[, , , , , , , ].
The wood is a good fuel[].

Propagation

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.