There are several species of Oak, some evergreen, some deciduous, but all more or less valuable and ornamental timber trees.

Among the evergreen Oaks are the well-known Holm or Holly Oak (Q. Ilex), from the Mediterranean region. It is perfectly hardy in the milder parts of the kingdom, and is very variable in habit, judging by its forms, such as crispa, fagifolia, fastigiata, integrifolia, latifolia, serratifolia, etc. The Cork Oak (Q. Suber), Q. acuta, the Kermes Oak (Q. coccifera), Q. agrifolia, Q. cuspidata, and Q. virens are other evergreen kinds.

The British Oak (Q. Robur) is the best-known deciduous kind. It includes several varieties, including pedunculata and sessiliflora. The "Golden Oak" is a form called Concordia, with golden-yellow leaves; and nigro-purpurea has purple leaves. In the village of Polstead, Suffolk, there is said to be a British Oak 2000 years old, with a girth of 36 ft. The Valonia Oak (Q. aegilops) is a semi-evergreen with a few varieties. The Turkey Oak (Q. Cerris) is a favourite recognized by its deeply cut leaves and bristly acorn cups. There are several varieties, including a variegated one, and one with very deeply cut leaves, laciniata. The Scarlet Oak (Q. coccinea), from North America, is a quick-growing tree with pinnately cut leaves about 1 ft. long, which assume brilliant-red or scarlet tints in autumn, especially in the variety called splendens. Sprays of foliage are largely used by florists. Another North American Oak with deeply coloured leaves in autumn is Q. rubra, to which may be added Q. palustris and Q. tinctoria.

With the exception of special varieties which are grafted, most Oaks are easily raised from seeds. Hundreds of thousands of the Common Oak are raised annually.