Each of the “islands” that comprise this exhibit is home to selections of oak trees from temperate regions throughout the world. Visitors can view examples of oak habitats from Asia, Europe and America that include shrubs and perennials associated with the environment in which they are naturally found.
Oaks make up the most numerous genus (450+ species) within the Beech family. The Latin for oak is Quercus. They are distributed throughout the Northern Hemisphere from the tropics to northern temperate regions, and have a life expectancy that can exceed 250 years. Oak lumber is used in furniture and flooring; cork oak bark is used to make cork. In the landscape, oaks are ideal shade trees. A wide array of wildlife relies on oaks for food and shelter.
Botanists identify an oak by examining several characteristics. The oak or Quercus genus always bears hanging male catkins and the pollen is distributed by the wind. The small female flowers always show three stigmas and both male and female flowers emerge on different parts of the same plant. The fruits are acorns with a “hat” (the capsule or cupula). Covering the cupula is a pattern of scales or concentric rings that is critical in identifying many oak species.
Oak or Quercus leaves can be quite diverse in shape and size, making it difficult to rely on them in the identification of the numerous Quercus species. The more well-known lobed leaves, prominent in Red Oak (Quercus rubra) or White Oak (Quercus alba), are not the only possible shape of an Quercus leaf. Many oaks such as Quercus montana or Quercus castaneifolia have leaves with a toothed edge and no lobes at all. Other Quercus have spiny leaves like a holly. In particular, many desert scrub Quercus from the Southern U.S. and Mediterranean share this feature. In contrast, tropical Quercus often have smooth edges with no lobes or spines but an elongated tip on the top of the leaf; these often resemble a larger version of a bay leaf.
The lifespan of the leaves varies as well. In the northern temperate zone, the deciduous oaks are the most common. They develop leaves in spring and drop them in autumn. However, many “evergreen” (or more correctly “wintergreen”) Quercus exist. These species hold their leaves year-round but, like most wintergreen plants, they normally drop them after two or three years. In other wintergreen Quercus such as Q. virginiana – Southern Live Oak, the leaves fall in the spring as the buds open and the new leaves emerge.