As you may already know, oak trees are not a single species, as there are approximately 80 different species of oaks that thrive throughout the Northern (and even Southern) Hemisphere. Many oaks are endemic to North America, and are often used to complement garden landscapes. In the past, Native peoples of North America used oaks both for nourishment and medicinal purposes.
From cold latitudes in the Americas and Eurasia, to tropical Asia.
Deciduous trees, (evergreen in some regions, shrubs in some areas). Leaves are alternated and usually lobed into about six sections on each side of the leaf. Flowers are very tiny, and without petals, with both sexes on the same tree. See images below.
Acorns can be eaten raw, though raw acorns tend to be amazingly bitter. White acorns, such as those of the Gambels Oak are the sweetest, but even they were sometimes too bitter to eat fresh from the tree. Therefore, acorns can be placed in slightly salted water for a week to remove the bitterness. Some other methods include exchanging the water very often or boiling the kernels. Some tribes used clay to mask the bitterness. Some sources report that powdered gelatine may also work, not that you will have powdered gelatine with you in a survival situation...
An interesting study showed that oaks produce acorns in "mast years". Masting is the process in which plants will go for a few years producing very few seeds, then produce huge quantities in one particular season. This prevents squirrel and mice populations from rising very high, since the annual output of acorns is unreliable. Then, by producing huge amounts of acorns in one year, trees can outpace the squirrel's capacity to eat the acorns, hence leaving behind some acorns that can actually grow into mature trees.
Oak bark tea is very good in the treatment for sore throats or inflamed gums, as well as the treatment of scrapes, cuts and burns externally. Oak bark tea is effective because of the high levels of compounds such as tannin and quercin. Interestingly, swellings on the twigs (galls caused by parasitic insects) contain as much as three times the amount of these compounds as healthy branches. This may be caused by the reaction of the tree in an attempt to defend itself.
Oak wood can be used to make good-quality hardwood handles for axes, digging sticks, and in modern times, furniture.
Some sources report that the bark tea is slightly toxic. The bud resin may irritate sensitive skin. Tannic acid is potential poisonous. Cattle and sheep have died after consuming large quantities of acorns. Remember that this article is no way is intended to offer medical advice; it is merely an interesting resource for those who would like to become more familiar with some useful plants.