Oaks (Quercus spp.)

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The Oaks (Quercus) are the largest genus of trees in North America. It is also among the most diverse with species growing nearly everywhere trees grow except the Northern Boreal Forest and the Tundra. There are about 60 species in North America north of Mexico.

Oaks are usually easy to recognize because of their distinctive, elongate, lobed leaves and their acorns, a polished brown seed sitting in a shaggy cup. However a large group of oaks, the so-called "live oaks" may not have lobes on the leaves and the leaves can be thick, tough, small, and evergreen.

Oaks occur in a wide variety of habitats. Some species of the Eastern Deciduous Forest are large, stately trees occurring in forests with rich, moist soils. Others are specialized for dry conditions such as rocky or limestone soils. A few species are most commonly found along the margins or ponds, streams, and swamps. Outside of the Eastern Deciduous Forest, oaks grow along streams in the prairie, in the drier parts of the Montane Forests of the western United States, and are common in the dry mountain regions of the southwest. Oaks are also among the dominant trees of the Chaparral region of California.

The oaks may be divided into three types; the white oaks, the red oaks, and the live oaks. The white oaks are recognized by the rounded lobes of the leaves such as the leaf shown in the bottom picture on the left. The acorns of the white oaks are not strongly bitter in taste because of low levels of tannins. Most species of White Oaks are found in the Eastern Deciduous Forest, although some species occur on the Pacific Coast, and one is a dominant tree of the Rocky Mountains.

The Red Oaks have lobes with points (as in the drawing at the top left). Technically the red oak group contains the live oaks as well, but because the two groups are so distinct they are separated here. The red oaks are bitter in taste with high levels of tannins. Almost all of the red oaks (as here defined) live in the Eastern Deciduous Forest.

The Live Oaks have small, tough, thick leaves. These leaves are evergreen and do not die and drop in the winter. Separating the live oaks from the red oaks is purely artificial and there are many species with characteristics of both live oaks and red oaks. One species of live oak occurs along the coastal regions of the southeastern United States, but most species are found in the Chaparral region of California or in the mountains of the southwest.