Any tree or shrub of the genus Quercus. The oaks have
alternate leaves, often variously lobed, and staminate flowers in
catkins. The fruit is a smooth nut, called an acorn, which is more or
less inclosed in a scaly involucre called the cup or cupule. There are
now recognized about three hundred species, of which nearly fifty occur
in the United States, the rest in Europe, Asia, and the other parts of
North America, a very few barely reaching the northern parts of South
America and Africa. Many of the oaks form forest trees of grand
proportions and live many centuries. The wood is usually hard and
tough, and provided with conspicuous medullary rays, forming the silver
grain.