Sheoak is the common name for the genus of Casuarina trees. These trees are supposedly so named because early English settlers decided that the Casuarina wood was very similar to oak, but weaker. Sheoak is most often used for fuel but is also sometimes used to make furniture. Many species are native to Australia and Asia, but they can be found in Europe and America as well. These trees are favorites to plant in Australia because they attract many species of native birds.
Evergreen, sheoaks closely resemble pine trees. Their foliage consists of extremely fine, textured branchlets similar to pine needles. When these branchlets are examined under a microscope, they have what appear to be little teeth. These teeth are actually the leaves of the tree, and the number of teeth on a branchlet indicates the species of sheoak. Further resembling pine trees, sheoaks also have seed cones similar to pine cones.
Sheoaks can survive in a variety of soils. In fact, the roots of the sheoak produce natural fertilizer by putting nitrogen from the air into the soil. Fallen branchlets located under the tree provide a natural mulch as well.
Additionally, sheoaks do well in drier climates because they lose very little water. In most plants, the stomates in the leaves cause a lot of water loss. Stomates are small structures normally located on the surface of leaves which open and close to let oxygen in and carbon dioxide out during photosynthesis. When the stomates are open, water escapes as well. In the sheoak, the stomates are located in ridges deeper in the branchlets, so water loss is minimal.
Casuarina equisetifolia, beach sheoak, and Casuarina glauca, gray sheoak, are both native to Australia and parts of Asia, but are some of the most widely distributed Casuarina species. With a straight trunk, which can lack branches up to 33 feet (10 m) from the ground, and grayish brown bark, equisetifolia is the most widely distributed species of sheoak, found in many countries worldwide. Glauca is the most salt tolerant of all the species and is also found in the United States, Israel, Egypt, India, and Africa. This species grows 33-49 feet (10-15 m) tall.
Sheoaks are used primarily for windbreaks and shelter belts in the US, partly because they initially grow very rapidly. The seedlings are often grazed on by cattle, and sheoak wood is ideal for use as fuel because it burns slowly and produces little smoke and minimal ash. In Florida and Hawaii, where most sheoak is found, wild trees are often considered pest plants.